Ditto on keeping at it and ditto on documenting everything...no matter how small it seems, document it.
Names, dates, the time of calls you made/calls returned/how long it took to return your calls. Everything.
One of my buds had a stack of paperwork about 18" high just because he was determined not to give them the satisfaction of giving up. He got 100%.

It took a few years, a lot of dogging 'em, some anger/few tears, but I got mine, too.
Somewhere within those years my attitude morphed into accepting it was a different battle, but one that I could...no, would win.
My expectations of them helping me evaporated but they were replaced by accepting offers of help from those who had been there/done that.
It amazed me how safe I felt again. Someone had my back.

In Peace,
Catherine