Over charged account

My husband took out a contract and he was supposed to pay R260 but to our surprise last month he was charged R359. 59 and when we called to enquire we told that the deducted R359. 59 because it was the first installment. Now they just deducted R847. 69. Please we need answers we can not afford to pay an amount we did not budget for. My number is *** with ID no. ***