Can our vacant apartment neighbor keep their heating off?

Our electricity bills have grown quite drastically into the winter months. 200 in October, 450 December, 740 in January. (No dryer in unit either)

We talked to our landlord, they say other tenants in our building are only paying around 200. So we started regulating our temperature after our 450$ bill. Used to do 68 permanent, now doing 68 when we’re home, 62 at night and during work. But still the bill went up.

We learned that our neighbor above is vacant. So I got suspicious and started checking their power meter. I’ve logged that they’ve only used 40 kWh in a week’s time. And 4 kWh in the last 24 hours. Absolutely no way their heating is on.

Is this legal? Are they required to heat their apartment to a minimum temperature? I believe all our heating is just rising into our neighbors apartment and doubling our bill.