RCS LOAN SETTLED

Good day, on the 25th of November, I settled my loan with RCS. I paid the full outstanding amount and sent the proof of payment through to them. At the end of November the Debit order, according to them, did no go trough. They keep on phoning me everyday and sending sms', despite the fact that I have told them the loan is paid in full. Please I need this to stop. This loan was only 6 months old!