The issue isn’t that OP asked for more money due to graduating, it’s that OP attempted to leverage a competing offer, that’s a shit practice. If you were unhappy enough to field other offers and you find one that you are happy to entertain accepting, just move on. Everyone likes to pretend that companies are just the nebulous entities but there are people on the other side and people tend to remember when they are presented with ultimatums such as “pay me more or I leave for x company”. In a perfect world that wouldn’t be so, but this isn’t that world.

Also expecting the company to advocate in OP’s favor and approach them when graduating for more money isn’t a solid strategy. Sure it happens sometimes but most companies don’t actively seek ways to increase their labor cost if not driven to do so.