I agree with Duck.
Asking on this board won't get you an answer as to what happened or why. I also have National General, I bought a new car (replaced one 5 years old) and my rate went up $22 on renewal.
I haven't had any claims but when I've called them with questions or to take out of or put into storage they have been very helpful.
I pay my annual rate in full when due. I asked what would happen if I paid half now and half in 6 months. They said my rate would go up $600 for the year. Wow...quite a jump but also quite a savings for paying now (which I did).
Talk to them and see what's going on.