@ChrisE Your very old meter probably measured in cubic feet. Modern meters measure in cubic metres. If they use the wrong conversions for your bill your bills can be 3.5 times too big, Check your detailed bill and make sure it does not say cubic feet applied to your new readings. Also the installer should have sent in the final reading from the old meter and the first reading from your new meter, they don't reset the readings on the new meter to match the old series.
If you divide your bill by 3.5 would that make sene then, it still seems very high for autumn usage.