Turn on the air/con and then go look at the meter. You should be able to see it moving. If it's not, something is wrong. Either the meter is somehow damaged and not recording power or it has somehow been bypassed.
I agree with notifying them via email, so there is a paper trail if they come back later to confirm that you tried to let them know.
I would set aside an amount roughly equivalent to what you are used to paying in the past. That way, if they figure it out and there is a bill, you can just write them a check.