Unfair billing and going against TCF

I've sold my car in August 2024. By October 2024 I've advised them that the vehicle has been sold so billing should not continue. They didn't respond to the email. I've called them numerous times but no-one can assist. They still bill me to this day - a year later and the more I tell them that I've informed them about the sale of the vehicle in October 2024 already - even sent them the email of October 2024 and the agreement of sale, they just continue to bill me and have in the interim handed me over to their attorneys. They're now saying that I should pay a cancellation fee - I've sent them the contract that they've given me in 2022 and asked them to point out on the contract where it states anything of a cancellation fee - no feedback from them AT ALL.