Dubble deduction

I am very disappointed. On the 26th of July I paid half of my account and Friday while paying the other half of the R1088 a whole R1700 was deducted from my account. Which means I paid double the amount. I tried to call with no success. I want my money refunded as soon as possible. Plus the I voice for this month also show the double amount. My question is why? I need answers and I need someone to make contact.