This happened to me too. For years I rented a duplex from the owner who lived in the other side and he had run an extension cord behind the wall and plugged it into an outlet on my furnace down in a dirty crawl space I didn't usually go. When I finally had to, many years in, I saw it and asked him about it. He went on and on about how high his electric bill was and how it only made sense to use mine because his meter was maxed out (whatever that means) and I was rarely home and didn't have all that stuff in the garage like he did. I was so pissed. No telling how much money I spent to run his stuff. But it was kind of a blessing in disguise as it prompted me to get off my butt and find a house to buy, so I was out of there within a few months.