Shortpayment costing me money

I need my paid up letter from you guys and you advised my debt counsellor that you erroneously short paid Wonga and you will make a payment on Thursday and issue the letter next week. That will be in November and it will mean I have to pay my debt counsellor an administration fee for November. Why should I be suffering financially for a mistake that was made by you???? This account was settled almost a year ago and the short payment was not picked up? I want my paid up letter by close of business!!!