Can't get into my Rover and the sitter isn't responding.?

I am wondering what you would do in this situation. This is the first time booking with this cat owner. They booked about 50 days ago and immediately paid. We did a virtual meet and greet last week where they chatted about their pet and they said they would leave a code for me (or a key under their mat...I am sad to say I spoke to them on a busy day and I usually take better notes and I just indicated "no key pick-up." I know if it is a code...I always ask them to message it to me so it is in our message thread. Either way, I found out that they live in a sky-rise apartment with a desk attendant and the attendant and first I couldn't get in the building and then when I did, the attendant wouldn't let me go upstairs without the owner escorting me. I explained that I am the pet sitter and showed the booking. They tired to call through the door system but the owner didn't answer. I had to leave and so I messaged them and then called them through rover asking if more details on getting in/letting them know what happened and that they may need to speak to their building to get me permission to enter. They have not answered. It is a cat and it has been about 24 hours since the owners left. It is fed once a day and so it was fed yesterday. I am not sure what to do here. I was thinking of giving it a few hours and if I don't hear back, calling Rover to see if they can reach out to the owners. I don't have a real cell-phone number...only their rover number. Any suggestions?