Why is it difficult to stop debiting from my account?

I'm utterly disgusted with Fidelity ADT, after cancelling my subscription with them in November the agent confirmed that they won't debit end of the month (which they did). I called countless times and keep getting the same story. Today, 24 December R717 is debited again including your yearly radio bull****! This is really annoying I'm paying for services I'm not using. I've explained that I've relocated and my tenant doesn't need your services. You have deactivated everything except for the debit order! I had planned that once I'm settled I'll continue with your services but you have definitely lost me as a customer. Money doesn't grow on trees, honour what you state on your contracts. And kindly refund my money for the two months you have debited. I'm utterly disgusted and disappointed!