TERRIBLE, TERRIBLE CUSTOMER SERVICE and no response from "supervisors" as promised

Our small family-owned business has used AT&T for 14+ years now.  We renew/renegotiate our contract EVERY October because most all AT&T customer knows they will easily double your price and say the promotion ran out if you don't renew annually.  Every year it takes several hours on the phone to get negotiated.  For the last FOUR years in a row, AT&T has managed to mess up our bill, conveniently overcharging us.  This has been the worst one yet.  We renegotiated in October, and the November's bill was wrong.  I called AT&T and the representative assured me she fixed the bill and would credit us.  Unfortunately, she credited us the amount we were supposed to be charged instead of the difference overpaid.  I have sent emails, used the "chat", and spent 3+ hours on the phone to try and get our bill BACK TO THE PRICE WE AGREED UPON!!!!!!!!!!!!!!!!  The reps keep offering to give us the current best deals, etc and all I want is the PRICE WE WERE PROMISED BY THE AT&T REPRESENTATIVE.  As this same situation has happened more than once, this time I was smart enough to get it in writing, via email, from the AT&T representative, with his email address.  The email contains the terms, order/renewal numbers, and all the information needed for the agreement.   The problem STILL has not been resolved. 

I have emailed the representative that gave us the agreement and have not gotten a response.   Then I went to chat, and chat told me I needed to go back to the representative that made the agreement.  After finally getting it through to the chat rep that the reason I was "chatting" is because that rep would not respond to my email about why my bill was not as promised.  I was given an email address, by the chat rep, to someone "higher up" that could fix the bill (the chat rep said it was all automated and he could not change it), AND ONCE AGAIN, HAVE GOTTEN NO RESPONE.  I was on the chat 3+ hours as well.  Next I called an waited on hold for 40 minutes.  The rep then offered the "best" deal as of now....I reminded her I ONLY WANT WHAT WAS PROMISED AND AGREED TO BY AT&T.  I was transferred to two levels up, and then told they would get back to me.  It has been FOUR months and AT&T STILL HAS NOT RESOLVED THE PROBLEM.  With what they have overcharged us, we should be getting March, April, May, June, July at no (additional) charge, as well as part of August.  This is absolutely ridiculous and absurd from such a large company.  I would switch in a heartbeat if there were another provider that had what we needed to run the type of business we do.  My recommendation is to use almost anyone EXCEPT AT&T.  Honesty and integrity you sadly will not find with AT&T.