What to do when I booked a deluxe villa, but got a standard villa? Only to realize this after checking out and leaving the property.

I just had a great vacation at a resort in Japan, however upon reviewing my booking I realized I paid for a deluxe villa, but got put in the standard villa.

I wish I realized this while I was there, but the rooms do look similar. The deluxe basically has a partitioned off sitting area and more square footage, but the standard is just one big room and no additional sections.

I’m just annoyed because I did pay more for the deluxe.

Do I contact the booking site or the resort directly? I don’t even know what anyone would do for me, but I just feel slightly gypped.