I doubt it would have been fixed during the meter swap. Meter swaps are very quick and easy they just pop right out. If the tech had noticed something a miss in the meter pan they would not have touched it and alerted OP bc the meter plan is the customers responsibility.

Your point about a neighbor using OP's electricity is very possible.

They likely still have it at their meter shop, if you would like it tested.

Additionally while it does happen it is rare that the meters are off especially by 2x. They are pretty rigorously tested during the certification process. The other possibility is an issue with NG's billing system which is more common of an issue. The MA DPU can likely help with that as well.

I don't live in Worcester anymore, however I may be able to help. I work for the NYS Department of Public Service, and we regulate utilities. Every state has a version of one, in MA it's called the Department of Public Utilities. I would reach out to them to help.

In NY the law is that a customer can request a meter investigation where the utility will pull the meter and test it in the presence of a DPS meter expert. If it was found to be out of spec you would be refunded the difference. I'm not sure what the regs are in MA but I would call and see.

Some of my other thoughts are that 800 kWh a month seems on the high side that works out to an average 1.11kW continuously. I had an issue where I would keep the fan on my forced air heat all the time to keep air flowing but it was actually using around 800-900 watts so I would check that l.

Also commodity prices for natural gas and fuel oils have been very volatile and high. Utilities pass these costs directly onto the customer, they don't profit off it or mark it up. Generally utilities will try and hedge these costs so that ratepayers are insulated from the volatility but all hedging can do is smooth it out. What I'm trying to say is that the utilities don't have much control over the supply portion of the bill.

I would also check what rate code/service class you are in, it should be listed on your bill. If you had a meter that tracked different periods you may be on a time varying rate which could affect the bill as well.