Researching my deceased fathers outsinding monies.....?

My father ped away 5 years ago. There was money left to my brothers and I when he ped. I was contacted by a company who said they were aware of monies that were in accounts. They want a finders fee, my father was in the service and had various accounts and securities. Does anyone kow how I can go about reserching this without paying a portion to a company?