no refund

I bought 2 x bamboo bodysuits on 24/12/2015, I chose incorrect size, on 29/12 I logged in to buy the correct size, but for some reason or other it would take me to the wrong size and this has been happening since 29/12 until yesterday 12/01/16 whereby I'd call the call centre everyday since then but my query is still not resolved and the stock has even run out. I've requested for a full refund and I'm told I can not be refunded in cash but in Groupon credit which I'm not happy with since it's their system issue that I have not been able to purchase what I wanted to purchase. I have sent numerous emails to the customer services to no luck. I am not a happy customer right now.