I have a POA and Health Proxy for my Mother. I had to get a verification letter from SS for her (dementia), SS refused both docs. Why?

(would be nice if we could edit our responses) ... That page, and subsequent ones, specifically state that a POA does not give authority to manage SSA benefits, and requires payee status. The FAQ page, with lots of answered questions: http://www.ssa.gov/payee/faqrep.htm

Hope that helps!

I'd start here: http://www.ssa.gov/payee/

Is your POA envoked? Have your mom's physician do this., the physician would have to declare her incompletent to make her own decisions.
If POA is alreade evoked, you might petition the court for guardianship. You will still need the letter from the physical referring to incompetence in making her own decisions. The latter should work for SS