refusal to cancel contract

i settled my contract in July 2020 and the contract was not cancelled as the lady at the store failed to inform me that i need to call and cancel it after settling it. April 2021 they started debiting my account again and each month its different amounts that are not on the contract. i requested for the contract to be cancelled since it has been paid up a year ago with no luck. my account is still getting debited as they refuse to cancel this contract. i sent an email without any response. the call center agents cant even tell me why my account is still being debited? what am i owing and what is it for????? i'm so Gatvol because this is affecting my credit score negatively......