ADT debiting my account after cancelling almost a year ago!

I was previously with National Security and cancelled my contract with National Security in May of 2023 and handed in their device in the same month. They however, ceded the contract to ADT and I have been charged for services I am not using, ever since. I sent proof of cancellation to Michaela Mahalie on 13 Sep 2023, and was assured by her that the cancellation would be escalated. This did not happen. I have escalated the matter 3 times and have not heard back from Fidelity ADT to date. National Security ceded the contract to ADT without my knowledge or consent and to date, the cancellation has not been effected and every single month I am debited by ADT. I am a pensioner and cannot afford to have this happen every month. Each time they debit my account I have to go to the bank and reverse the debit, which negatively affects my credit profile as well. This is unacceptable!