My brother just past, he gave me the policy number and what I thought was the name of the insurance co. The name of the insurance company is wrong. How do I find the comp. By the policy number?

There is no standard for how insurance companies number their policies, so no way to know the company just from a policy number. If you are the executor of your brother's estate then I suggest you look through his financial papers to see if you can find a policy document.