Refund is Ridiculous

I placed an order with MRP Sport online. Two pairs of running shoes. I paid half the amount with a birthday gift card and the balance with my MRPG account card. When delivered, only one pair was there and I had to call your customer care line to query. I was told the other was out of stock and that my account would be refunded. This did not happen, so I tried emailing and received a reply saying it would be done.

I have now received a refund voucher via email. It states it is only valid at Mr Price Sport apparently?! So not only was the balance not returned to my MRPG Account (which I used to pay!) as I was told it would be but I get a voucher that I cannot use elsewhere? So now my account is higher and my birthday gift card is replaced with a limited voucher for a division of your company that I rarely purchase at and will probably not use in future. Why am I left worse off because you didn't have stock of an item that was stated as in stock online?!