Museo del Prado Private Guided Tour with optional Reina Sofía

We booked this tour expecting it to be two hour private tour. We met our guide promptly at 9:45 and entered the museum at 10:00 am. Our guide was excellent at explaining many of the works however, there were some rooms that we skipped as the museum started to get more crowded. After she showed us some of the rooms I was hoping that she would lead us back to the rooms that we skipped but instead she took us around to the area by the gift shop and the cafe and told us we were welcome to look around on our own. We sat down to take a little break and I looked at my watch and realized that it was only 11;30 and not 12 noon when the tour was supposed to end. By the time I realized this, our guide was no where in sight and I had no idea where she went. Anyway I did complain to Viator about this issue and the tour operator refused to issue any type of credit. They claimed that we received the full tour and our guide stayed with us the whole time (which she did not). However, After a lot of back and forth Viator did make good and gave us a credit for part of the tour which is what I was asking for. If you book this tour I would verify with the tour operator exactly how long the tour is so there is no discrepancy. I have booked many tours through Viator in numerous cities in Europe and this is the first time that something like this has happened.