Sorry to hear whats happened to you, I can totally understand why you feel let down.
This isn't an official Virgin Media website and therefore we can only offer advice here.
We do have very long lead times at the moment and although it wasn't your fault, if VM moved you forward they would have to cancel someone elses install. The Supervisor was being honest I guess, even if you didn't want to hear it. I obviously don't know the "tone" of the converstion of course.
One thing you could try is emailing the CEO office and seeing what they can do for you? Or possibly speaking to Customer Relations on 150 "thinking of leaving us"?