Fridge freezers are designed to be in a room that is always at a temperature of 10 degrees Celsius, or above. This is in accordance with the European design standards referred to as the 'climatic classification' of your appliance. If your fridge freezer is in a cold garage, out building or unheated area of your home it may shut down during the winter months, resulting in the freezer contents defrosting.
This is not a technical fault with your machine and an engineer is NOT required, simply heat the room or re install in a warmer part of your home.