As Emperor said, it's probably a difference in brand name. I've noticed that I can wear certain sizes from certain brands but not from others. Tbh you're probably best returning the jeans if you can, stretching them seems like a bad idea to me lol. That or you could try to lose a few pounds, but considering you're wearing 30x30 it sounds like you're already a pretty lean guy.
edit: Oh, same brand name, my bad. I still recommend returning them for a larger size, probably your best bet.