They sold me a broken product!!!!

In April 2020 I brought a 3 bar heater from the Game at Promenade Mall, it was the last of its make on the shelf on the day when I made the purchase and it didn't have a price on, as I had to go around the store to look for an assistant to tell me the price. It's now August 2020 and the heater has been sitting in its box unused as I'd found an alternative heater at home. Upon opening the heater now in August 2020, I have found 2 of the 3 bars on the heater broken - much to my shock. Thinking back now, it was never opened and checked at the store when made the purchase. The heater has a 3 YEAR GUARANTEE as stated on the box, it's never been used and this is easy to see. But now my predicament is that I have lost the slip because I purchased it months ago and didn't think I was being sold a broken heater. I want to return it, get my money back or an alternative resolution. I'm very shocked that all this time, Game stores sold me a broken product. And it was not my responsibility to check if their products were intact, that's what their staff is there to do. I trusted that the product was fine and took it home unknowingly. I know that if I go to the store and try to return it, they will give me problems about not having a slip from 4 months ago - despite the fact that it's clear that this product has not been used and the packaging is still intact. I'm not looking for a fight, I just want another heater or a refund or an alternative option. I'm still in disbelief as I'm a frequent buyer at Game and I've never experienced this before.