Open Question: Insurance Claim Problem?

Ok so they hit and run my husbands truck and well the guy who hit the truck had insurance. We filed a claim,adjuster came out to take picture and look at the truck. Now they sent my husband a check to fix it which is $2500. We found someone that can fix it for $400 and we wanted to keep the rest of the money for ourselves. Now the insurance company is calling us for a quote on how much the damages are going to cost. Would be a fraud not to sed her an invoice of the real cost of the damages? Or really just ignore the insurance calls and not send them nothing because they already mailed the check to us in his name... Someone please give me some advise on what we should do Thanks!