Billing acct ending in 0741

My name is Rick Hatmaker, my account number ends in 0741.  I am writing you because I don't know who else to talk to.  I called in Feb of this year to cancel my internet account with ATT,  and after 4 months, numerous calls and chat sessions, multiple promises from the loyalty dept, I am STILL being billed!  It baffles me how a company as large as ATT could not handle such a simple request! It's getting absolutely ridiculous!  I do not want this to affect my credit, so I am considering legal action if this is not resolved immediately.  I have spoken to way too many people for this to be continuing.  It is nothing short of harassment! Please let me know if you will be able to help me, or if I should proceed with further action.