contract cancellation

i have had the worst experience you can think of, my contract finished August 2022 and i called in January 2023 to cancel it till this day its still not cancelled and they keep debiting my account telling me that and will take 30 days for the migration from contract to prepaid now they telling me it will be cancelled on the 27 April so that they can debit my account AGAIN next month............when i want to speak to a manage or team leader they are not available or busy........ which is utter nonsense. if i don't get this sorted i will definitely go to the Ombudsman