Life Insurance – France

Hi Everyone, Happy New Year, this is definitely a complicated situation and I was hoping to get some help pertaining to claiming a life insurance policy. My uncle had a life insurance policy in France but it appears that he did not have any listed beneficiaries. He was not married nor did he have any kids and only had one sibling (My Mother), he died back in 2003 and when my mother inquired about claiming the life insurance, the brokers at the insurance firm told her that she could not and she had to prove that she was his sister. (however the hospital was quick to give her the body for funeral arrangements but refused to give her his jewelry….). I think they were given us a hard time since we were Americans. Apparently, my mother tried other ways to claim the insurance but was unsuccessful. I was a little kid when this all happened so I wanted to see if I can help now, I was wondering if it’s still feasible to claim this insurance and what steps should be taken, would this be worth the effort? I am greatly appreciative for any advice or tips.

ADDITIONAL INFO: I should I added this detail, my uncle changed his both his first and last name as well.