Supersonic incompetence, claims after 4 years

I’ve cancelled my Supersonic account on 18 November 2020. An immediate payment was made to settle the account. It took about a month for them to release the line. Supersonic claimed the account was not settled and handed the account to the Nimble Group for collection. All evidence was provided to them but now they rep****: ‘ I have been advised we need a verified document that account has been indeed closed’. If Supersonic failed to close the account, how can it be my problem? Every month Nimble keeps on adding fees to the account.