Unauthorised debit order deduction

I've cancelled my subscription on the 1st of December 2019, and the consultant old me that they are taking the last Debit order at the end of December as I need to give 30 days notice. Which I agreed to and understood. At the end of January, obviously didn't budget for the debit order to deduct because it's been cancelled and the last payment did go off. Yesterday, I got an sms notification that a debit order went off.. now I don't have enough money in my account to have my actual debit orders go off, because I've just left enough money in the account for the debit orders.

This is now after they took a double premium in October.

I am so disappointed and frustrated with CellC.