It is possible that your display unit was loaded with incorrect tariff information, Sago
I've been trying to think of what 'error' within the display unit (not the actual meter) might result in the reading you got.
What is your daily standing charge for gas?
It's a wild shot, but it occurred to me that perhaps the decimal point is wrong, and the figure should perhaps read 64.689 pence, which could, conceivably, equate to two days' standing charge, or even one day's if standing charges have rocketed even more than I thought,
I am probably way out in my thinking, but that's the way my mind works - when I am faced with a problem like that, I always try to think of possible explanations before I contact someone. Surprisingly often, it helps me to spot any bull** that they might then try to fob me off with.
Anyway, good luck with sorting this out, if you haven't already done so. 