Why does she scoff at me, ignores me , criticizes me?

we had a fallout ONE year ago. i have behaved myself since. shes just a work colleague we never dated. i used to have feelings for her but i thought she came off a bit immature and i let her known she was not my type & undateable in my eyes. the fact is when i try to have any type of normal friendly conversation she acts like the above and it hurts.