Automatics are usually thirstier than manual gearboxes.
The colder weather also doesn't help with consumption.
My diesel in the past could get up to 1000 miles on a tank (1600km), but last fillup with 54 litres got less than 600 miles (1000km).
It's just the time of year, there is more usage of electrical equipment ie the blower is on to defrost the car, the heated rear screen is on, the headlights are on, the heated seats etc all these in themselves increase fuel consumption but added to get her is a real drain on the battery and the engine is colder so takes longer to get to temperature, the alternator is working harder to replace power used, which makes the engine work harder and more fuel is used.
Putting a better grade fuel in may help if not already doing eg Shell V-Power Nitro, BP Ultimate etc.
These burn more completely as they are also at a higher octane (may also give better km/l and better acceleration).
More power, bigger explosions more heat etc engine warms up a little quicker.
I don't think it's anything you or the car are doing wrong, just the time of year.