Unable to view DVR recorded shows

Twice in the last two weeks and at least one other time in the last few weeks I have recorded a show and then been unable to watch it.  I have used restart, system refresh and xfinity assistant with no change.  Why am I regularly and consistently unable to view shows I record?  Why should I keep paying you for a DVR I cannot rely on?  By the way, whenever I waste my time with xfinity assistant and it fails to resolve the problem (and it always fails to resolve the problem) it always ends by saying a a repair technician will contact me and a repair technician has Never contacted me, ever.