Billing issue

AT&T cares? Really?? Two of my payments have not been credited, and I am receiving threats that my account is being suspended. My bank has already faxed documentation that the two payments in question were indeed deposited by AT&T. I was assured by a service rep by phone  that this would be examined, and my account credited. Then I received a notice of cancellation. I called customer service and was given a fax number to fax my documentation -different from the one my bank faxed to. I tried for an hour to fax to that number; it sent back a busy signal the entire time. I have plenty of evidence that my account is paid in full, but nowhere to send it (I did send copies to my local AP address by Certified Mail). At this point I am ready to give up on AT&T, and seek redress through my State's Attorney's office or the Interstate Commerce Commission. Then, once my account is settled, I'm ready to seek another supplier. AT&T cares? Show me. I have been a loyal (paying!!) customer for over 25 years - and I get this treatment?