I live in a two story duplex, yesterday the other unit's electricity went off, the electrician diagnosed that somehow their neutral path is not coming from the pole so he connected the neutral connection from my meter to their neutral (changing some wires through circuit breaker). He was doing it through circuit breakers as we don't have a main breaker. So my question is "with the live wire from his meter but a neutral path through my meter, is my meter is being used?"
TL;DR: CALL YOUR ELECTRIC UTILITY ON THEIR EMERGENCY NUMBER
It sounds like you live in a duplex with dual services -- in that case, call your utility ASAP. What the electrician did was a very dirty hack that will not pass Code muster, and likely screw with the electrical metering -- it will also break in interesting ways if later on the utility puts the two units on different transformer secondaries.
BTW -- an open neutral is an emergency situation, as it can easily be a fire and/or shock hazard.
If the terminal on the meter for the neutral that was joined with your neutral is the outgoing terminal, then your meter if smart will read the reaulting current from your neutral and his neutral. If he has more load than you and he uses single phase, then your meter will read very fast. But if it was joined in the incoming neutral terminal, then your meter will not read his neutral energy.