****mers and horrible service

Wonga has debited me for the instalment wheresle I made manual payment on the online app which shows on the Wonga app.and has updated ,after Wonga has updated that I owe them R512,they went and debited R2368 which didn't make sense because my manual payments of R1400,R2400 and their debit order of R2126 and 2368 had been debited which now makes a total of R8568 now has been credited to them and I only owed them R5000 in total.I now want them to refund my balance and they asking me for proof of payment which the bank can't provide me cause the payment was made through the online Wonga app,my question is why do I need to provide proof when the didn't ask for proof of payment when they updated the other manual payment I urgently need this refund to pay my daughter's school thing and I've made this request since last week Wednesday and till this day they are not willing to assist.