Unreasonable waiting times

I was due to attend a PIP Assessment at 1:15pm today as I'm moving from DLA (after 18 years) across to PIP. Got myself physically and mentally 'kind of' prepared for the meeting only to be called at 10:30 and told that there could be up to a 3 hour wait!!!!! I have a spinal injury which prevents me from sitting for longer than 30 minutes maximum plus I suffer from moderate anxiety/depression and this would have put all of that through the roof! I advised them that I could not physically wait around for that length of time and rearranged the appointment only for them to turn around and tell me that I wouldn't be able to rearrange the next appointment if the same thing happens. I find this totally unreasonable and inhumane to expect people with disabilities to wait around in a strange place for that length of time! Has anybody else experienced this please as I am so upset and doubly anxious and depressed now?