Continuous cancelled appointments

I have scheduled 4 appointments to get my Home security system fixed but it keeps getting canceled. I have called several times and am told they will send a technician out. The rep schedules and a few days later it's canceled. I have taken off of work to get this done and of course, I get a message stating my appointment was canceled. I am tired of this service.. I pay so much money and can't get Comcast to come out and repair my home security. I am at my wits end. Does anyone know how to get a technician out?