Hi, my name is ***** ***** I have been in the home improvement and repair field for 20 years. I will be very glad to help you today. There are a few issues this may be.
The evaporator may be iced up and the heater that melts the ice on it is not able to melt the ice in between cycles as it should.
This is caused by a few things. It could have been caused by items in the freezer blocking the vent. It could be that the door was not completely closed a few times. It could be that the setting is too high or it could be that there is a mechanical issue.
To fix it it is quite simple. Remove all items and unplug the power. Leave the doors open and allow it to defrost for at least 24 hours. Before restarting clean the inside really well, especially the bottom of the fridge where the condensate drain is.
It seems there is a leak on the coolant. It was either what I had suggested before or the worst. If after defrosting and cleaning it never got cold then the issue unfortunately is that the coolant has leaked out slowly. Adding coolant and fixing the leak can be quite difficult to repair and only licensed technicians can purchase and apply the coolant. It will not be economically reasonable to repair. I am very sorry about your fridge.