Hire OSS, isn't he an attorney?

Good advice on leaving IRS out of it entirely until ONLY when needed.
Ask to speak like said to higher up at USAA and see if they can help.
None of my business and don't need to divulge, but where did all that 350K or so go do you think? Very odd, that is a huge amount of dough for most of us to just disappear.
I know it is too late and you tried, but wouldn't a drs. written note explaining he was mentally incompetent to handle affairs set in your POA before he died??? I think USAA overstepped their legal limits and you need to fight them, but talk to them nicely first from higher up mgr. You should have every right as POA to get all information concerning your dad's funds.
And here I thought I had issues when I found out 2 grand (of which I will let slide) was given by my mom to my older brother to help put down on a loan on a pickup truck for his son. I asked mom a few months later after it happened since I balance her checkbooks every few months (she only writes out 4-5 checks per month just basics is all) and she said they would pay her back, but will never happen.
Not looking forward to when my mom passes and have to deal with her belongings (tons of junk in the house sort of a pack rat). I won't have money issues to deal with like you, or so I hope in case she has to go into assisted living, etc. since 4-5 grand per month is insanely high and will get her bankrupt and then have to sell the house as well, sure hope that does not happen, but could.
What will be worse is my mother in law, who is a ton richer than my mom (both dad's passing), has high value (guessing 500K and over) stocks in AZ far, far away that her brother set her up with some investment company am sure making that investor rich as well charging insanely high fees. I'm not a huge stock/bonds type of guy since not rich by any means having the means to put that kind of dough into 401k, etc. , but once she passes hopefully 20 years from now if lucky, my wife has POA and will be getting those stock back to us. But, what to do with them, who knows??? I'm not a spend thrift kind of guy, but a bigger house and storage in the country away from everyone would be nice but won't need that much once my kids are gone in 5-10 years. Traveling is nice, but not a huge travel type of guy like my older neighbors going to AZ for the entire WI winters.