Pretty much the same thing happened to me. I booked a guarantee balcony cabin on Ovation eight months before my 8/26/22 sailing as one person, and was assigned a studio. I expected an obstructed balcony view but not the small cabin. When I called (well, Costco TA called) RCCL insisted that I had not paid a single supplement. No resolution, and that is the cabin I will be sailing in. Lesson learned: I should have taken a screen shot or somehow printed the booking prices on BOTH a solo and a double occupancy mock booking on the day I deposited. The problem was this time --I could not prove that I had paid a solo supplement. Prices were a lot lower eight months ago but all RCCL did was assume that there was no solo supplement based on current pricing.