Yeah, just bring in that box and tell them it isn't working and to give you a new one. Give the people at the counter a vague description such as "Stuff that used to work, like some pausing and rewinding stuff, and I'm tire of rebooting it." They'll just pull a replacement off the shelf and hand it to you.
Heck, I WORK for a cable company and it took a visit from a technician in my own home telling me "This box is really old, you could have brought it in for a replacement a while ago and never had these issues" for me to realize that electronics get old.
Two other thoughts:
It could actually be a software problem + box problem. Sometimes guide updates get pushed through automatically, and even thought the software vendors and cable company test it all before they roll it out, something goes wrong with specific hardware. If it's a new problem (meaning that the engineers haven't got wind of it yet) the front line tech support is going to be clueless that something went really wrong and they'll try to solve a bad problem with simple solutions.
The cable company has no say whether or not FF is disabled with the On Demand stuff. What is available, when it is available, and whether or not you can FF is entirely under the control of the content owners. The cable company is just the waiter who's job it is to get you your meal efficiently, Disney/Fox/NBC are the chefs who decide what's on the menu and how they're going to prepare it.