MTN billing for cancelled contract!!

Good Day, I had 2 numbers linked to my account. I waited the full 24 months to cancel the 1 contract as I no longer require that number. The contract ended on the 21 May 2021. I had a debit order go of my account this morning for the number that has already been cancelled. This is highly annoying as MTN has confirmed the number was cancelled. If I do not check my account balances, I would have not known a debit order is going of my account for a cancelled contract. I expect this to be rectified ASAP and the debit to be refunded to me. Regards, Sameer