Midway Neutral disconnects whole house supply
You have a broken neutral, and that is an emergency.  Stop using anything right now that is downstream of that neutral break and having voltage problems!!!

Those appliances meant for 120V could see 240V, and appliances made for 230V could see 400V.  This could fry them and start a fire.  

Seriously.  Now! 

Then go back and thoroughly go through all your wiring, especially anything that guy touched, and find that neutral problem and fix it.