This was my fourth time staying at the Crowne Plaza Belgrade and I was a bit disappointed with the service level on this trip. Upon checking in, I asked if it was possible to upgrade my room (for an additional payment, not complimentary) to a higher category, but I was told by the receptionist that there were no other higher category rooms available, despite that when I checked on hotels.com app, there were plenty of rooms available. When I confronted her on this she asked the manager to step in who initially claimed that the app was wrong, and no other rooms were available, but in the end gave some poor excuse about having "Indian guests under quarantine" in the hotel and that the rooms were on the same floor as the quarantined guests therefore he didn't want to put any other guests in those rooms. This excuse seemed odd and I don't understand why the hotel was not interested in upselling me to a higher category room. Next when the key the receptionist gave me didn't work in the elevator, she insisted that I wasn't inserting it correctly and, rather than just making a new key, walked to the elevator to show me how to use it... when she tried to use it, surprise, surprise, it didn't work for her either and she had to make a new key, what she should have done in the first place instead of insisting that I was not inserting the key into the elevator properly.... it was just a lot of unnecessary wasted time and really poor customer service.