Offline system problems

On the 22nd December I paid my Edgars account at Mall of The South whereby I received a slip. Sometimes in in January I received an sms that alluded that I have not paid my account I then went to Southgate Mall with my slip. I was told that the payment did not reflect on the system and they made a copy of the slip which was supposedly send to HO. A week or so I then received another message that my account was in arrears. I called Edgars and the lady who helped told me that they have received the query and they are busy with it. End of January I paid my instalment and only to find that the account is still in arrears. I called the Call Centre and the lady who helped me told me that I must pay the outstanding arrears to keep my account healthy otherwise it will reflect at Credit Bureau as a slower payer. I don't know what more I must do because I have a slip as proof that my account was paid but Edgars seems not to know how to help their customers. PLEASE I DID PAY R700.30 INTO MY ACCOUNT IN DECEMBER 2015