Handed over for cancelled contract (BA***)

I cancelled my contract (BA***) in August 2020, paid the cancellation fee and retention confirmed that they cancelled it. However, I have been receiving billing and calling in every month (staying on the line for over an hour) to tell you to stop billing me because the contract is cancelled. Every time I make a call, I get apologies and confirmation that the contract is cancelled and closed. The next best thing I am getting handed over...for what? I am tired of calling your retention department every month and getting stupid reference numbers (latest:***) with no action.

Please remove my name from your systems and train your people to do their job.