Cancelled Contract, still being charged 2 months later

I have been trying for an entire day holding on for someone to answer the phone in the accounts department, with no joy! Your accounts department must be in utter shambles if they're too busy putting out fires that they aren't able to answer a call.

I cancelled my contract on 25 November 2021, and two months later am still receiving accounts to pay. FOR WHAT???? I even received a acknowledgment email in response to my cancellation with a reference number. Please can someone get hold of me!!!