Reimbursement for incorrect charges

Posting this in hopes that someone from ATT can assist regarding Case # CM20221005_154793153.

I have been seeking help with this case for about the past 19 months, but it is still unresolved.  I cancelled FirstNet cell service in AUG 2021, but was being charged monthly well into 2022.  Finally, someone from ATT was willing to talk with me in OCT 2022 and assisted in stopping the payments, which were being automatically withdrawn from my bank account.  At that time, I was informed that my “adjustment request has been approved and a credit has been applied to your account.  If you have access to the Premier website, adjustment will reflect online within 24 hours.  Note:  It may take 1-2 billing cycles to appear on an invoice.”

It is now late April 2023, and while the monthly payments have stopped, I have not been reimbursed for the approximately 13 months I was being charged for cell service I did not have.  I called ATT again the other month, and was told there was nothing they can do, as I “no longer have an account.”  However, the entire reason why I had to dispute charges for over a year was because I did not have an account and was being charged anyway.  It seems too convenient that ATT can charge someone without an account, but cannot reimburse someone without an account. 

Desperately looking to get this solved after 19 months.  Can anyone assist?