UNAUTHORIZED DEBIT

These guys have no idea what they are doing in their accounts department. I had owed an amount in November last year, the amount was paid and I re-activated my account. On 30 April 2019, my account was debited for an amount that is not my usual debit order amount. I queried this and was informed my the call center agent that this amount was in fact the amount that was outstanding in November. Apparently, the amount that I paid in November was allocated to my December and January invoices. The November amount was not for these months, it was for an old outstanding amount. Now 3 months later they wake up and choose to debit my account. The call center agent could not explain to me why their accounts department had done this. Pathetic service. He escalated this to his manager and I said I would expect a call back. He had the nerve to ask me for what?!