Cannot get anyone to help getting an appointment rescheduled

I had an appointment within a 2-4 PM window after spending over 5 hours trying to get my services with Xfinity all working properly.  They never showed up, and after another 30 minute call, someone promised to find another qualified technician and call me back at a designated time.  They never called back- in fact, I was promised 3 call backs and never received them.  I have been on calls that have lasted 90+ minutes, put on hold for long periods during these calls, calls were disconnected... the list goes on and on.  I am a 30 year customer with Comcast/Xfinity and have been told so many conflicting things that I am about to start over with a new provider.  I cannot spend my life trying to get someone to actually follow through with anything.  Supervisors are no help at all.