I think the military might have messed up causing my dad his life insurance? Help?

This is complicated...not sure if anyone will be able to help. My father seperated from the army in 2002 he thought he was discharged. I believe he canceled his SGLI due to bad advice thinking he could convert to VGLI because he paid on his life insurance for over 30 years he wouldn't just up and cancel. Problem happened when army did not fix in computer he was discharged. My dad moved with me to another state thinking he was discharged. My dad got ill couldn't go to VA doc had to go on base because it still showed active. He wasn't able to file for VA benifits or VGLI due to it. We found out he got cancer and he ended up in and out of Hospitals. He died in Aug of 2004 and SGLI said his seperation date shows as July 2004. One month before he died. --- what do I do I think they cheated him out of his life insurance and messed up his paperwork. (I know I'm asking late but I'm just finding out info about all this now because they wouldnt tell me much when it happened)