Failed claims process

My mother passed away in 2018, she is a policy with jet stores underwritten my metropolitan. I tried to claim but could not was told to get a letter of authority. The process got delayed and only got it last year, tried again after they gave me a letter back in 2018 that there was money, Now they want statements and all sort of things to do the payout. It is frustrating because they are the ones that gave me proof that there was funds available what more do they want?