Telkom data ..overbilled n to refund will take the whole month

Telkom overbill me for nothing..my bill is due on 2 May n they charge me R399.44.which was double amount for my monthly payment.but if it was me as a consumer reversed they money they could overcharged with 1 installment as a penalty..but beacause of me now i dont have power to give them penalty hoooo poor consumer being victimized