Online order - Cancelation /Refund delay

On the 30th of June I made an online purchase for a heater only to find out that it's not in stock however the payment was made successfully online. I have been calling Builders warehouse for the past to weeks as I haven't received any substantial information. They keep on telling me the same thing over and over again that they will get back to me but I had to call again and explain everything repeatedly to different call center agents. I then requested them to cancel the order and give me a refund as their service is horrible to say the least. Even canceling the order seems to be a mission and a half. What do we have to do to get online service and our queries handled professional? The order is still showing in progress since the 30th June.