Account debited for a loan that is already paid up

On the 13th of May I made a direct deposit to settle my debt earlier than the arranged date. On that very same day I sent an email requesting for a debit order to be canceled as I have paid up my debt. Surprisingly the debit order was not canceled, R1354.60 was debited on my account (25/05/24).... I need my money back!!!!!!!!! The settlement letter dated 15 May 2024 clearly states that I have settled my debt in full.