I had something kind of like this happen to me last year.

I booked a newer 4 pts at a C&P rate over chat because SPG was showing availability, but I wasn't able to book it. When booking she offered a suite for 3000 pts + $90 and I agreed to those terms in the chat. A month or 2 later I looked at the actual reservation (and room rates) and saw that the suite was now listed for 3000 pts + $30 (the same as a regular room) and that my reservation said the same. They ended up trying to charge us the higher cash portion when we checked in, but I had a printout of the confirmation and they changed it to the lower amount then (no long phone calls necessary). It was a great deal!