Unacceptable customer

I called RCS on 8 March 2018 to obtain a settlement amount for a loan. The amount was given and I paid it immediately. A month later I see a debit on the my account again. I called them again (waited 20 minutes before they answered). They then claimed I paid in the wrong amount. I checked my records and I definitely paid the amount they stated.

They then said that they would need to check the recordings, but could tell me how long this will take. In the mean time, I keep getting sms's telling me my account is over due. I also see now on the date I paid in the settlement amount, that new charges where added to the loan and they have repeated these charges again for April and May 2018.

I am now concerned this will impact my credit record, despite me having settled and not being in arrears at anytime. This is not acceptable to expect customers to wait indefinitely before someone decides to sort out an issue.