Double Charge

Hello, i had purchased an item from Builders Express, which is part of Massmart. when paying i was told that my card didn't work. i then used another card, only to find that that the card did work. Meaning that i have been double charged. I have been fighting them since the 27th of last month for them to return my funds to avail. first excuses were that they cant find the funds, the other that they are using now is that the banks wont allow the transfer. i am out of pocket for almost a month and no one seems to care.