Sleep Country Canada review: Purchased wrong size mattress

Accidentally bought the wrong size mattress for my son (bought a twin size) before we converted his crib to a bed it ended up being a full size bed frame, not twin. My mistake. The conversion kit was bought years ago so I didn't think it'd be a full size. Called sleep country the same day we bought mattress but because it's a floor model we can't exchange for a full size. I wasn't told this before or after purchasing, it's just on the receipt. It's still wrapped in plastic and has never been slept on, and you can't help me out? Called customer service. The reps were friendly and understanding, but I had to call three times over a week before getting an answer. They said management decided it would cost 30% for an exchange and 65$ fee. I just can't afford it. I'm already in a lose-lose situation because a full size mattress is going to cost more than a twin, so I need to pay additional costs when I exchange, on top of 30% + $65 for a mattress still wrapped in plastic and never slept on and that I inquired to return in less than 24 hours, like really? I'd get it if I was just making a stink and wanting a refund but I'm not. Id love to keep this mattress the quality and brand is great, but I need a bigger size. And now I'm stuck with one that doesn't fit when I know they could help me out. I just don't have the money. If I did, I'd just do it at this point so my sons bed could be put together. I could do maybe 10%, but 30% PLUS 65$ fee? Thanks alot. I will not be doing business here anymore and I guess my son will have to sleep on a mattress on the floor.