I don't know whats wrong, I use to resist ice spells because I am a ice person but I dont resist anymore. Don't you always resist attacks that are from the school you are from. I am level 16, do I have to wait for my resistance to go up or what?
A lot of gear specific to your class will involve some resistances for your school of magic, but not all do. Check your hat, robe, and boots, as well as the ones you used to wear. Most likely you removed at least one item that had ice resistance and replaced it with something that did not.