Accumulating monthly statement.

Edgar's keeps increasing the amount of installment and the overall balance stays the same Nomatter how much I pay each with each month, in Feb they said I owed R39 and I paid twice that amount, and I used R200 on the 437 credit they gave me, but when the statement came at the end of Feb it was R139, I paid R140 and I didn't use any credit. This month the statement says I owe R179 and they can't explain to me why I owe that much. This is ****************.