Appointment Cancelled Twice - Don't Know Why - Still Having Issues

I have an X1 4k DVR and three small boxes in other rooms. One of the small boxes is not working; the rest are fine.  It is showing an error code (RDK-03036) even after going through the troubleshooting steps multiple times.  After going through the troubleshooting steps originally, the app had me schedule an appointment for a service tech to come out.  The next day, I missed a call from Xfinity (I was in a work meeting and unable to answer).  A few minutes later I got a text saying that my appointment was cancelled.  A little while later I got a text saying that there was a disruption in the area and that Xfinity is working on fixing it.  I later get a text saying they have fixed the issue and I should try my service again.  I check and the box is still not working.  I go through the trouble shooting steps and eventually it has me schedule another appt. for a service tech.  The next day I get a text message saying that my appointment is cancelled; this time with no explanation.  The box is still not working.  I just need to get a tech out to my house to take a look at the box.  Why does Xfinity keep cancelling my appointment.  It's now going on 5 days since I first tried to troubleshoot the box and get a tech to come look at it, and Xfinity won't keep an appt. to send someone out to look at it.  How can I set up an appt. that Xfinity will keep and not cancel?