Paid up letter not provided despite settling an account based on a discount that was offered.

I paid an outstanding Student Loan and was offered a settlement discount of R513.17. I paid the settlement amount but they have not contacted the bank to give me a paid-up letter despite many e-mails and calls. They have handed the account over to another collection agency that is now demanding payment for the outstanding amount (discount). I have made followed up by phoning and sending e-mails to the e-mail address provided namely *** but this has not been sorted out despite promises by the people answering my calls.