Poor service

I have settled all my account with them on the 15 Feb 2019. The problem I have one of my account reference number was wrong with one number so I called them to rectify the situation and they asked me to send a proof of payment for that account with my id number and correct reference number so till now they called me to pay I explained to them that I made a mistake with reference can they reverse the money and I will pay again with the correct reference number but till today no one is calling me back and tell me what to do because the account number is theirs they can rectify the issue and send me the settlement letter. Can you please take over.