It's not unusual to see your gas bills increase during winter, however I can understand your concern given the amounts. Can I suggest that you start by checking the meter reading on your bill (18,678) which was taken on 13/9/2018 against the current reading on your meter? If the reading on your meter is now higher than this, then this suggests that the meter reading is correct.
In addition to this, do you have gas ducted heating at the property? This is a common cause of high gas bills during the colder months.
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