What happens if my insulin freezes? Why can't I use it if has been frozen?

when it freezed the molecules of water and the medication seperates. As soon as it is defrosted the insulain becomes degrated and will not work the same at all.

I use Insulin 2o IU a day, have kept it in the refrigerator, & in normal room temperatures, never have frozen it, kindly do let me know if you get any answers, plaease.