ATT still threatens collections due to their error, help

We depend on our cell phones as the life blood of our business. Regrettably after not getting any resolution with technical support (dropped calls, technical issues for 2+ years) and spending hours out of our busy day in the attempt to resolve the issue (with no real improvement and lost revenue)  I regrettably decided to cancel our service after 9+ years of being loyal customer.

On 6/12 I called ATT to disconnect and cancel my service after almost a decade of loyal business. After I inquired about ATT waiving the early cancellation fee (I was more than half way through my contract and because of continued poor reception ) the rep (reps name omitted for privacy) in a gesture of good will agreed to waive the fee if I remitted any outstanding balance on the account. The customer service rep took my payment (paid with a credit card). The rep confirmed that the account was closed and no further balance or future balance was due.

I then received a bill on 7/27 for $313.85 stating that "we have cancelled your wireless service because your account remains unpaid and threatened collections.”

I paid half the bill on 8/11 because we were threatened by ATT collections

(even though it was ATT’s error).

The facts:

• ATT did not cancel the service because of an unpaid bill. I voluntarily cancelled the service and remitted any outstanding balance due.
• Secondly, ATT  continued to bill me for  service I did not have as I cancelled the service and my account on 6/12.

• On 8/11 I called ATT customer service (customer care or whatever you call it) and spoke with customer service rep, (name omitted to protect privacy). I requested an explanation to why I was billed for service after my account was clearly cancelled on 6/12 (after the phone was out of use and cancelled) the rep did not only fail to answer my question but became defensive and combative. When I requested an explanation from Mr. (name remitted to protect privacy) why I would receive a letter threatening collections when it was obvious the letter was clearly incorrect the rep told me that my service was suspended for nonpayment (repeating himself), which is completely false as it was obvious I cancelled the service myself on 6/12 and the cancellation fee would be waived.

• The letter from ATT was written to imply that my service was disconnected due to nonpayment (and not because I cancelled it) which was errornous (not the case) and completely  falsehood.
• When I requested an explanation for the erroneous collections letter the rep proceeded to tell me that my service was suspended for non-payment. When I demanded an explanation (again) why ATT would send me such a letter (as it was obvious it was incorrect), I again explained to the rep that this was an error as I clearly cancelled my account and service permanently on 6/12).
• When I again requested an explanation and asked the rep to confirm when (and who) cancelled my account on 6/12. The rep agreed that I (the customer) voluntarily cancelled and terminated the cell phone service on 6/12/15 and that it was not possible that my account was still active on 6/12/15.
• After factually addressing the inconsistency and error, the rep changed his tenor and proceeded to tell me that my account was suspended.
• When I asked for an explanation how my account could be suspended after I permanently cancelled and closed it (and paid all outstanding usage charges due for the last month of service) the rep became defensive (again) and deflected my question by explaining to me that ATT does not waive early cancellation fees.
• When I asked for an explanation to why one service rep waived the fees and now I am being made responsible for the charges I was then rudely interrupted and explained (more like lectured to) that ATT does not waive cancellation fees (third time).
• Again I requested an explanation the rep became even more combative and rude (fourth request to explain the inconsistency)
• After requesting a valid and truthful additional explanation (fifth request) to why I was being treated so rudely and purposely lied to (i.e.: billed for the early cancellation fee after it was waived and charged for an additional month for service after my account was obviously closed by me on 6/12) the customer service rep did not answer my question and preceded to tell me I was being charged for the extra business cycle anyways.
• I than demanded an honest explanation why I was deliberately being mislead and without warning the customer service rep hung up on me.
• When I asked why I was still being billed for an additional month  of service that was obviously cancelled the rep would not truthfully give me an explanation.

This is not the service I expect from a large and company that prides itself on customer care such as ATT.

This issue has caused me unnecessary stress and financial hardship on my family and busiess. ATT has threatened to send my closed account to collections due to an error on ATT's end. What is upsetting is that after almost ten years and tens of thousands of dollars spent I was treated this way.

I respectfully request the following:

That the errors be corrected and the payment (half of the $313.85 due) be refunded to my credit card and the balance on my account corrected to reflect a zero balance owed.

The above is a snippet of my conversation with two representative claiming to be from the "executive office: "

I was initially called by (name removed to protect privacy)   (336 area code) (claiming she called from the executive office of the CEO of Att).  I was then called by another person claiming to be in the "executive office" named (name omitted) (201 area code) .

When I returned her call today to resolve the complaint she claimed to not have the complaint or support documentation that I sent ATT through the BBB as well as the certified letter sent to the executive office (per the Texas office) which seems very questionable (how did she then know about my complaint in the first place?) considering she called me in the first place to resolve it. 

I was than told I was to call (name omitted) in the executive office  (area code 201) and she was not only unwilling to assist me resolve this issue she refuted and challenged my complaint. 

After asking (name omitted) how she came to the decision  (after explaining what occurred as indicated in the complaint) she continued to repeat herself without explaining her reasoning. Moreover I was supposed to speak to someone in the executive office and was called by two different people that were not only unwilling to help me resolve this issue but were argumentative, unhepful, insincere, and unprofessional.

 Why ATT would behave this way is beyond me and serves no purpose. Moreover it does not make much business sense to treat it's customers this way.

What I want is what I was initially promised as stated above. I wrote a professional and respectful complaint letter and all I got was continued combatitiveness with no resolution.

What baffles me is despite my detailed (2+ page) complaint letter with names of reps, dates, and times ATT finds it necessary to behave this way after 10 years of loyalty. 

Thanks for your help.

Steven