I'll list problems as I read through the post.
1. Too cold. Probably your main problem. They will not eat if they don't think their body is warm enough for their digestive enzymes to work. This is the same reason humans have a core temperature of 98.6. The only difference is the snakes depend on us to provide the proper temperature. Try bumping it up to around 92.
2. Using gauges. These are considered very inaccurate. A widely available model of AccuRite with built-in hydrometer and outside temperature probe is the most recommended.
3. The condensation in your tank could cause mold. Just something to be aware of and keep a close eye on.
4. When snakes go off feed, I've never seen it recommended to just stop trying. He may have decided he would eat sometime in the winter and you never gave him the opportunity.
5. The energetic cat definitely would have made him nervous. It's good that you got him away from it.
6. How long has he been in his new home? At least a week of complete and total alone time is recommended after something like that.
I don't know much about feeding issues, but I'd give him some time in his new home to realize he's safe. That is if you've addressed the temperature issue. In the long run, 30 gallons sounds like a bit much for a ball python and he may have been insecure from the start. If this problem persists, you could try putting him in a sterilite tub from walmart if you can transfer heat sources, etc. Just the tub, substrate, thermometer, hide/s, water.
Good luck.
I'm slow tonight....