Debiting account on cancelled contract

I called to cancel my long expired contract in October. I understood one more month would be debited. I have just been debited again. It took me a week to get through to the retentions department only to learn my account had only been temporarily put on hold in October and I still should pay, even though the sim was at least deactivated when I called. So the call centre agent didn't bother to cancel the account properly at the time. I and now left having to pay 2 extra months for a contract that hasn't been used and was deactivated anyway. The agent I spoke to this morning said an investigation will be launched and I'll hear from someone in 48hours. Let's see...