My late ex husbands retirement account

My ex-husband and I were married 1987 and divorced 1995. When I left him I left with just my clothes on, I did not even get my jewelry box in the bank that belongs to my mother. I just want to get out of a bad hurtful marriage. He called me later to sign a divorce paper which I signed. I never went to divorce court. Ten years later he died, I did not know about it and just last month I got a letter from the state of California that there are some money on a money market that was on my name. When I went there, I found out that there were 2 accounts, the other account was a retirement account but they are not saying anything about the retirement account. They told me to write a letter withdrawing half of the first account and the other half of the first account will go to his estate since I am divorce to him. Can you tell me anything, or any advice for me. I remember he has a retirement account but I don't look at his finances when we were married.