Claims not being paid after numerous calls/emails

I submitted a claim with onepet and paid for it using the debit/credit card that they provide as part of the cover. However I have now received numerous SMS's and emails stating that I have an outstanding balance. I submitted the proof of payment as well as my pets microchip numbers (more than once!!) as requested by onepet yet this issue has still not been resolved. I have spent hours on the phone with onepet trying to resolve this but still nothing has changed. Absolutely useless customer service.