DVR storage limit suddenly changed?

Hi, I have the Xfinity premium DVR plan and to my knowledge this allows 300 hours of recordings. So, my DVR recordings indicated 37% full the other day. The next day, it showed 78% full. I didn’t add any additional recordings overnight. This makes no sense. How does my DVR go from not even half full to almost out of space overnight? Here’s a current breakdown of my recordings:

120 Hours HD quality 

15 hours of non-HD

So, a total of 135 hours of recordings. It seems as if I’m being shorted of the extra 150 hours that’s included in my plan. If I only had 150 hours of available recording this would make sense why my DVR is almost full. Of course I contacted customer service and they were totally useless and unable to reasonably offer a solution. Anyone have any ideas?