Settings for Candy Fridge Free?

Candy CD-9 Fridge Freezer
When I set the Knob inside the Fridge to 4 the Fridge is showing 5 degrees and the Freezer is only showing Slightly over minus 5 Degrees and once the items in the Freezer thawed out. When I set the Knob to 5 the Fridge freezes the food and milk and is showing approximately Minus 5 Degrees and the Freezer shows minus 15 Degrees. Could you please advise me what to do. I have tried putting the Knob between the 4 and 5 setting but it could go either way and it is either too cold or not cold enough.