Refund in full amount

Good day Would you please Assist. I have a contract with Vodacom, My monthly bill is R 292.99. Debit order go through on the 25 of every month. On the 25 of May debit order didn't go through and on the 21st of June I made a payment of double installment for may and June which was R 696.94 through EFT. And on the 25 of June same month Vodacom debited same amount of R 696.94 which was already paid for via EFT. On the 26 of June I called Vodacom requesting for refund of R 596.94. They requested for bank statements to clarify the payments,I sent the statements. They said double charge is appearing on their which simply mean refund is successful. I was told refund will take 7-14 days to process. Today I called Vodacom again to check on the process. I was told that I'll be given a half of amount that was debited the remaining will be for upfront payment for the month of July however it wasn't part of conversation I had with one of their consultants. I requested refund to be full amount not R 348.47

Would you please assist on the matter.

Thank you