Complain TFG ****mers

TfG trading as Markham is ****ming us,1st October my due amount was R335 balance was R4878 I paid on the 9th October R350 and my balance was R4543,25 October balance due isR440 and balance is R4777,they are failing to explain where R234 is coming from since they say their books are closed on the 12th of every month.it means I will never settle my debt with them as the balance keeps increasing not decreasing