I am really sorry you are going through this.
I know I sound like a broken record.
I'm at the same place I was in the begining.
The pump broke, you have no idea what caused it and neither do they.
Detent, valve open, valve closed, bla bla bla. You attest you opperated with the valve in the correct position, they say you did not. They say they tried to fix two times and did not notice the valve setting until the third attempt, and take a position it was like that all along, and I say a pig just flew past my house, more bla bla bla.
No different than me saying you stole money out of my wallet and you saying we've never met, me saying you grabbed my but in the elevator and you saying "whaaaat ?". Just hearsay (not sure that's the correct word).
It broke under warranty and needs to be replaced under warranty, no evidence to the contrary. Humm, maybe the cause was the faulty o-ring that failed, fragmented, got into the relief valve, fouled it, and contributed to overheating. There's a good theory for you, and no easier to prove or disprove than the crud they are saying.
Hopefully you paid via credit card. Challenge the charge, make it clear you paid in order to obtain your property back, the charge was forced and in no way did you concur with the charge.
Turn the tables and let them sue you for payment, go to court, lay it all out, and say "pound Sand".
Here I am in my basement office and just thinking about this is irritating me.
Sorry my friend, again, share this dealer's story with everyone and anyone you can.
Joel