Terrible customer service and refusal to pay my refund

I went to the Game store and requested the settlement amount on my RCS card. I was given the amount and settled the account that day, only to realise they didn't take the debit order into account that was paid a few days earlier and I subsequently paid too much. After multiple calls and emails and going to the store they have still not refunded me. I phoned the call centre and spoke to 3 different people. The last indicated that they need to speak to the finance department and will call me back within a day. This was now a week ago and am I still waiting for the call as well as my refund!!