Fridge only unit did not cool

Question

Fridge unit did not cool. First repairman said evaporator needed to be replaced. First repairman returned with a second repairman who said Freon level was low. Added Freon and fridge now appears to be working. Is this a reasonable fix to the problem. There was some icing around a tube at the back of the fridge which they said was blocked. Why did the Freon level go down ? My warranty will expire shortly is this a stalling tactic until it does ? Should we be worried about leaking Freon, do they still use Freon in Fridges ?