Harrassment and exploitation

Good day im now tired of the harrassment i receive from this company each and every day. They claim i owe them .the funny part i went to jet and asked for the remaining balance to settle my account because i noticed being paying installment but my balance kept on increasing in july i owed R1500 i payed R400 to my surprise i was told the balance is R1368 i was so surprised. Notice i wont finish to pay it off decided to settle it went to store asked for remaining balance payed it off even have the slip only to be told after a month a owe R235 i asked for what because i settled the account and have the slip.so im really tired of the harrassment. Thinking of opening a case against this people because they been destroying my credit score with the false information really tired and dont know why they calling me 8 times a day a i payed them offf.