The lines can be hooked directly to the power side of a set of lugs
instead of to a breaker. This is totally against all codes, but it
happens. Find wires from the power company to see where the first
panel (maybe only panel) is located (next to or backed up to the meter
usually). If you cut off the main breaker to all panels close to the
meter and the plug is still energized, it is either hooked directly to
power or coming from another source (This happens often in apartments.
They get wires crossed all the time from one apartment to another.) If
hooked directly to power, you will have to call that $200 electrician.
You must have this dangerous situation taken care of, since this can be
a real fire hazzard.