Warning: Centre HiFi dishonest retailer

I want to issue a warning in this holiday shopping season to be careful where you buy your electronics. I purchased an expensive TV at Centre HiFi in Montreal and want to return it two days later. They lied to me and told me it was new. I discovered while opening the box that it had been opened and it is clear that it was used as either a store demo or previously returned by a customer. Upon testing it I discovered that the colors are off and the image skips frames every 10 seconds or so.

They refused to issue a refund and offered store credit. I don't want to buy anything there again and want my money back. Has anyone had a similar situation? What can I do? Thanks