Two Missed Windows, Tech Lied -- How To Escalate

We have a problem with no sound from our Uverse STB that has required a tech visit. He was scheduled to arrive between 1 and 4 PM yesterday. At 3:45, we got a text saying he probably wasn't going to make it.  We called the support number back and were given a scripted reply that said there would probably be a 2-hour delay. We heard nothing more. My wife called at 6:00, and we were told the tech had waited outside for 20 minutes, got no answer, and left. We were monitoring the phones and looking for a truck in the easily visible residential street the whole time and got no call, saw no truck. It appears the tech lied. The call center rescheduled for 1-4 PM today, but I have little confidence this will turn out any better. The call center is clearly staffed with people who give scripted replies an cannot escalate issues, whether or not you say things like "unacceptable". I'm also concerned we may be billed for a non-existent "missed call". How can we escalate problems and get a resolution? I sent a PM to Customer Care but have had no reply.