Do you have any material proof that this stay really happened? Your word only will not do much for the hotel or Hilton Corporate ...

A screen capture from the digital check-in / digital key perhaps? As it was a reward stay, are the points still deducted from your account? Do you remember (specifically with names) with whom from the hotel you spoke?

Until you are able to prove (yes, the burden of proof lies on you) that your butt was actually in that bed, nothing will change I am afraid - it is as simple as that.

And you can forget about escalating, no one at Hilton will move their finger for your missing one-night credit, I have heard and read about much worse happening to lifetime diamonds and Hilton not giving a dime ...