Microsoft Xbox Double Billing Refund Nightmare

On the 20th of December we purchased an Online Game from Microsoft Xbox. They double billed us for the Game (2 x R269.70). When we requested a refund, they cancelled the game and informed us that we would be refunded the full amount of R539.40. After a lot of queries, phone calls, mails etc. We have still not been refunded. We were told to contact our bank as they needed to release the funds and we were told by the bank that they can not help as no refund has been made and despite numerous requests, I have not received proof that the refund was paid back and customer care is useless. They are very quick to take your money, but not willing to give it back for a billing error and I don't even have a Game. I will never purchase an online game from Microsoft Xbox again