Hi Asllan,
in both of your threads here you have given some basic information that suggests common faults experienced by many people here - but I think this is getting confused with other posts regarding coolant levels from other users and some linguistic issues.
1) Get a new battery, because the old one is not giving enough voltage to crank the car in cold weather.
2) If the car does not go > 60˚C on the driver thermometer reading after several km driving hard, change the thermostat - if the thermostat is broken the car's engine will never get warm. If this has no effect with the temperature reading on the dashboard, replace the coolant temperature sensor as well. 1.4Tdi engines run very cold, so unless the thermostat *AND* the temperature sensor are working perfectly, the driver temperature gauge will remain on 60 degrees all day, especially in cold weather.
If the car is cold (<90˚C water temperature) - or the sensor is broken so the car thinks it is cold, it will use large amounts of fuel because the computer believes the car needs more fuel to warm up quickly.
This is not the same as losing fuel, or losing coolant mentioned in another person's thread - these descriptions suggest a broken pipe or bad seal.
Is your car also losing coolant (ie, water level falling)? You have not mentioned this precisely before.
To help with answering the question of the temperature sensor, VCDS or a computer reader connected to the car may help further by giving more accurate diagnosis of your problems. If you give us more information, we can help better.
Good luck!