Double payment

I have a contract with cell c for over been with them over 10 years. They debit on the 15th of every month, so seeing that I was paid on the 14th as the 15th of August was falling on a weekend, I made a direct transfer to cell c. Then on Monday the 17th they debited again. I then called them and app**** for the money I paid to be paid back. They are taking forever to return the money and its inconveniencing since that money was for something else.