The game required 1gb of ram, so pretty much iPhone 5c and above, iPad Air 1 and above and I think Mini 3 (maybe 2?) and above. Sounds like it's a RAM issue. Unfortunately there was no way to get the textures small enough without sacrificing the look of the game.
I'm not sure how to do a refund -- it's something apple does, but I know they do it. You'd have to contact them. Sorry!!