Live tv will not rewind after watching a DVR recording or a streaming service

After replacing my old cable box with a new one I noticed can no longer rewind the live tv after exiting a DVR recording or streaming service. I have read many Xfinity forum messages but Ive seen no solutions. I have also been to the brick and mortar store 3 times to switch my box. I called and spent 2hours on the phone trying to fix it but nobody's really told me what the problem actually is?? This was a useful tool and if it's been taken away at least tell me why and perhaps discount the DVR option since it no longer does as much as it used to!! Anyways my last option before I change providers is to try and direct message through this forum.(which you can't do until your u make a post) so here it is!!