Why would i be refused car insurance?

have fleet insurance that covers any driver over the age of 25. I had an accident 6 months ago which i know wasn't my fault but unfortunately i wasn't insured at the time as the payments had been cancelled. The other party is trying to claim from my insurance company, is this allowed as i was uninsured and secondly the insurance company are now refusing to insure me, anyone else but not myself, is this allowed?