Xcel Energy Over charge/incorrect billing Clovis NEW MEXICO

I rencently sold/moved out of a house in New Mexico. The last bill I received, for the dates I was still living in the home and for about a week after I moved out, was about $170.  The house sat empty with every circuit breaker in the service panel turned off with the exception of the furnace, which was set to about 50°F. The water heater circuit breaker was off, the refrigerator was unplugged...nothing else in the house was running.

A month after I moved out, I received the monthly bill showing the house had used 1000kWh more than the month before. An empty house used more electricity than one with an entire family living in it? I sold the house a month later. New owner transfers the acoount and I get a final bill of another $100 for only half the billing period.

When I called to inquire, I was told that there is something drawing power in the house that I wasn't aware of. My question was how could anything be using power through a service panel that is 99% turned off. Xcel claims they actually read the meter in each month prior to my leaving, which is what my bill states except for the last bill, which says it was estimated.

Estimated based on what? The previous month? So nearly $300 in electricty, for a month and half, from a house that is unoccupied. Something is very wrong with this picture. Even when I ran my A/C all day/night in the summer, the bill was never, ever this much.