Business Phone - Incorrect Charges causing increasingly larger billing issues

What does it take to actually cancel an optional service and have it removed from our bill? In a moment of insanity I added business auto attendant to our phone service (even though when I signed my company up, I was told that was included, whatever).  Well I was never actually able to set it up due to technical issues on AT&T's end (their words, not mine).  After giving them a month to fix it, we decided to use Google Voice instead for this feature since...you know, it actually works.  I called and asked for them to 1) remove the auto attendant charge from our bill for the previous month since we hadn't been able to actually use it for that whole time due to the technical issues on their end and 2) to cancel the service going forward.  Of course they told me no problem, pay the full amount now and we will credit your next bill.  Fast forward to November, charge is still there.  I call again (keep in mind each of these calls takes like 45 minutes between all the steps, waiting, language barriers, and attempts at upselling) and again am told it will be taken care of, give them a few days, they will change the bill, I wait as long as I can but they don't change it so I adjust the numbers myself and send payment for the correct amount.  Now it's December 18th, bill arrives, charge is still there as well as a leftover charge from November because of course they never removed it.  I call again.  They tell me they will handle it and get back to me.  Later that day I get an email saying it will take 48 hours to change my bill.  48 hours goes by, then 3 days, then 4, so I email them back and crickets.  This is during the holiday season, we are a large nonprofit animal rescue so we are just a little busy.  December 26th I decide to send the payment just to be safe (due on the 28th and my treasurer insists on paying via checks).  I go in on my day off to get it all done and bring it straight to the post office to mail myself.  Now it's January 3rd and I notice the payment hasn't posted to the account.  Mail can be iffy around here so I call and they say they haven't received the payment.  I explain that we always issue payments right when we receive the bill but that it had been delayed because of then and after a ton of back and forth I'm told they will waive the late fee IF I pay over the phone at that moment.  So I do and accept having to deal with my treasurer on the back end of all of this.  Of course, the check I mailed magically arrived the very next day, putting a credit on my account for the January payment.  Fine.  Except not fine.  They posted the late fee on my account anyways AND are still charging for the business auto attendant.  I reach out over chat only to be told they will waive the fee but only if I pay it first and then let them credit it to my account again.

What is it going to take for AT&T to remove these simple charges that they keep TELLING me they will remove?