Multiple TV channels & on demand not working at all.

Several of my channels give me error codes and haven't worked since I've had the service.  Some of them work every now and then but rarely.  A few months ago my Cox on demand function stopped working altogether won't even open the main screen.  I've had a service technician come out about the random channels not working but was unable to figure out the problem. The technician had mentioned something about a possible filter on the box outside but couldn't get to it due to a tree?  When the On Demand issue started i dealt with customer service over the phone for sometimes hours and brought me through tier 1, 2, and 3 of problems with still no resolution.  Tired of paying full price for half the service.  Any help would be appreciated.