Why is Dec 22 40 days? That is 11-12 days over any previous months. That is just under half a months worth of gas tacked on. If you also count the days for each reading from Jan 22 to Dec 22 it comes to 373 days so that is over 365/yr. There are too many days and depending on which days they are over counting (cheaper cost months before the increases) they are overcharging you.

Plumbers are capable of looking over the inside of your building, unless it contains many apartments I would check with them, and determine if the lines are going to the right meter or if someone is connected to yours. Speak to your landlord so that they can gain access to where it comes into the house, the meters and where each apt is connected to the meter.

Back in the mid 90's I got a notice that I was being shut off for non payment. I had been sending payments with the bills I received. When I called them, it seems they had the lines mislabeled for my apartment since the lines were a cluster.

I would call a plumber first, make sure you are paying for only you. I would also do as you are doing reading it every day and take a picture, each time, too of the meter for proof. I would call the gas company and discuss the irregularity of the days cited on you bill. I would also check that every window/door is closed and tight. Beyond that, I think they have us all by the short hairs at the moment.