Balance query

Hi..I'm very disappointed with the above store ( Lewis Store)last monthin June,my balance on the account was r2440.86,then I paid full installments of r866.74,balance suppose to come down to r1573.97,and at the end July I'm suppose to pay again full installment of r866.74,and the balance suppose to be r707.20 that will be paid end of August,,and now I get the statement today says my balance is r2270.65 , which I totally don't agree, I'm disappointed,can you please intervene,help me to sort out this matter .Thank you in advance.