It takes a long, long time of repeated seasonings before cast iron skillets become non-stick. Just re-season it and next time just put some oil in on top of the stuck food and wait until it softens enough to be scraped out with a spatula. Then sprinkle some salt in the pan and scour it with the salt and some oil~some people use newspaper to do this but paper towel or a rag will be fine. Oil it again before storing.
I use a cheap paint scraper/plastering thingie with the sharp corners rounded off. No food has ever withstood its scrapy power!
As Jay says, creating a good seasoning layer takes time, it's not a one-off thing.
In my experience, the best seasoning is animal fat. I should eat more meat, for my pan's sake, of course