I would hold off on cashing it, just by personal experience. Often what the check is for is the fixing/damages. Normally the bodyshop gets the money, but sometimes you get the money and then you have to pay the bodyshop.
The only other thing I can think of is that somehow you are getting a "settlement" for other damages like whiplash. Still.. if you cash it, in a way you are accepting that you will never pursue them in the future for problems related, although usually you have to sign a form. I'd just keep on trying to call them, or even ask the bodyshop to see if they get direct payment from the insurance company.