Wonga loan settlement

Wonga and their lawyers have been sending me emails and making debits for the loan that I've paid up already and sent proof of payment to them more than 3 times already but still they haven't cleared that debt instead they harras me with emails saying I have to pay. I've called both also to confirm that I've paid they also comfirm but after few days they send me an email that I've been handed over.

Wonga I've paid you on the 19th of July. But still you say i owe you even when the money appears in your records, what more do you want from me as i can't keep calling and explaining this n sending proof of payment every other week.