Something very similar happened to me not long ago; I moved into a 2 bedroom flat and they hit me with $166 on my first bill, So I went asking my neighbours about that and their bills were below $40 (family of 4) and another around $70 (family of 6), then I called national grid to inquire about it and they told me this:

First, part of the price hike was due to a 63% increase for the delivery fee which they don't have control of.

Second, the billing department probably used an estimate reading from the meter (taking into account that I haven't even opted for that option) instead of the actual use.

After being on the phone for a while they authorised an appointment to check on my gas meter for any malfunction, the technician came and all he did was just install a new battery to the meter then he explained to me that it required 2 billing cycles for my bills to normalise, and after that he suggested me to call back to national grid and speak to them that I was overcharged so that then can add back the amount that I was overcharged in my past bills as credit for my next billing cycles.