Number of guests in room. Are we being scammed?

Hi, we are a group of 4. We booked 2 rooms for all our hotels during our trip. In some places, when we got to the hotel they said we actually booked 2 rooms, but for one person in each room, so we had to pay the difference. it seems unlikely to us that we made the same mistake in more than one reservation. And if we look at the booking order, we see 2 adults per room, but also 1 adult in a different section.
IDK, I'm confused, and it's not the first time we've travelled, so we are starting to think there's some sort of scam going on.
Anyone encountered this problem?

by IDK-Tanga