Appalling service

I cancelled my contract in December 2023 and was informed that it will be cancelled on the 18th January 2024. I made my last payment end of December 2023, yet they debited my account in January and there were no funds to cover the debit order. They debited again in February with double the amount they tried to debit in January. Now I have an adverse listing on credit bureau because of them. The matter has been with their legal department since May this year.