Cellphone Bill

I am beyond furious, Cell C has made me pay double for my cellphone this month. I called them at the end of April to let them know my purse was ******, made arrangements to pay three days late, they were quick to assist with banking details and all. I have since then sent my proof of payment FIVE times and today they debited the amount for a second time. I called and was told nothing can be done. This is also the second time they have made me pay double!