No online account. Can't terminate service

I am your land phone customer of 35 years in my present location. I have land phone service from another provider for over a year and have been trying to terminate my AT&T landline for almost a year without any access to an online account and ability to manage account. When I enter my phone number or my account number my data is answered "invalid." Last summer called to cancel my AT&T phone service and although the rep (Maria) said she placed my termination order, it was not terminated and I have no paper or email record of my request. The billing continued on my fixed rate subscription plan. Then last October I went to the DC public office with my paper billing and the rep tried to find my account online but could not access it either. I asked him to help me put the account online but he told me he can't help as he has no record of me as a customer. I asked him for a paper record of my request with him and he said he could not provide it as I was not a customer. So the billing continued. Then in March 2024 I disputed your charge with American Express where my account with you is on auto pay. Based on the facts above AmEx rejected your charge. However, instead of your learning from my written concerns you continued the billing. The amount has been only about $50 every three months but now that the billing is over $100 I have received a termination notice, with no hope of recording my dispute with you.. Yes finally the service is being terminated but (1)I was billed in error for a year and (2) if I pay I'm afraid you will just keep billing me on auto pay or (3) you will ruin the credit of someone who has been an ATT customer for over 50 years!