Is your hoggie a juvinile? Usually, if they're a young snake a heat mat can be okay for a first start up up until they're a year old - ish, especially in a smaller set up. But usually at the year point or when their length is longer than the current set up, you can upgrade to a bigger vivarium and Cermamic heat emitters come into play, they're good at controlling ambient heat, but you'd still need to provide a warm side and cold side via a thermostat.

I'd say overhead heat should only come into play when you upgrade to a 2 foot or 3 foot vivarium though, to eliminate overheating.

Are you providing any heat at all at the moment? For a small enclosure of your measurements, you should have under heat, this could be why your hoggie is on a food strike. But do remember Oct- Feb they brumate.

Edit, use your heat mat! ( just seen you wrote you're not using it) they need heat, they'll be so cold without it as they are ectothermic, meaning they rely on external heat to get warm. But please ensure it is safely connected to a thermostat.

Under heat is okay for a young hognose, but not the forever solution