Your reservation says one thing, but the hotel (or airline or rental car agency) says something else. Worse, each one repeatedly pins the blame on the other. I see this often when an airline’s scheduling change affects a reservation or when I’m asked to sign a rental car contract with different terms than what was booked.
How to avoid this: Remember that the online portal is still your travel agent. You gave them money, and they pocketed a commission. The buck stops with them, and their guarantees are meant to assure this. For example, Expedia promises that your travel “will meet the descriptions on our site and in your itinerary…or we will work with our partners on your behalf to find a solution.” If your travel agent keeps telling you to call someone else, you will need to remind them that this is their job. As a last resort, you can threaten a chargeback if necessary.