Poor service from accounts and customer services department

Terrible experience with Truworths, my account was paid before the due date. I made a mistake of using my ID number as my reference number instead of account number. Immediately after making payment I emailed customer services who stated that they would send it to the accounts department. My account is showing in arrears. I contacted customer service and Lizelle advised it would be rectified. I am now receiving several sms and calls from the debt department stating that if I don't make payment my account will be on hold and it would affect my credit score. If this is not rectified immediately and I notice that my credit score has dropped, I will be taking action against Truworths and contacting the credit ombudsman cause this is pure negligence. My account will accumulate interest for late payment which is not fault. Fix this!