Almost the same happened to me every third time when I was staying in one of Hiltons worst hotels; Hilton Springfield
I booked the GOV rate online but when I checked in I was presented with another rate. First time I didn't see that when checking in, and it was lots of hassels to correct it.
Seems that Hilton Springfield sweeps their bookings on a regular basis, and rebook GOV rates to company rates. My company have a negotiated rate, which of course is higher. How can they even do this, I mean I book in one rate and they decide to switch me over to another? Beats me!
Luckily I'm not going back there anymore!