Fridge freezer problem. I have experienced a major problem with my fridge freezer which is now 3

Question

I have experienced a major problem with my fridge freezer which is now 3 years old. Everything seemed to be working as it should apart from not freezing.This is a side by side model and the freezer section is not freezing. It is just cool but not cold.The fridge side is not as cold as it should be and is just slightly cool like the freezer.Where would we begin to try to pin point the cause?Thankyou for any assistance you can offer.Mike