Refuse to refund money for online purchase

I have placed an order online at Mr Price and waited almost 3 weeks for it to be delivered to my selected store. I have phoned the help service to cancel my order and I spoke to Joshua Pather. Joshua told me that my money will be paid back within 14days. After that period my money was still not paid back. I then send a number of emails where I was asked for my banking details. After sending my banking details a number of times I was given a voucher which can't be exchanged for cash. I am not interested in a voucher or buying any more clothing, I just want my money back. I am still a student and I need that money.