There's a lot of frost in my freezer. What stopped working?

First thing: make sure it’s closing properly. If something is preventing the freezer from closing tightly, that’s enough and a hell of an easy fix.

Yes, I checked that it is closed properly and nothing is warped. I should add that the temperature display is showing the correct temperature, and there are no leaks. Everything looks normal except for the frost.

Is it the freezer on your refrigerator or a chest freezer?
If it is frost free, there should be a timer and a heating coil that keep the frost from forming. One of those may have stopped working.
I googled info about how frost free works and got this info.

A frost-free freezer has three basic parts:
•A timer
•A heating coil
•A temperature sensor

Every six hours or so, the timer turns on the heating coil. The heating coil is wrapped among the freezer coils. The heater melts the ice off the coils. When all of the ice is gone, the temperature sensor senses the temperature rising above 32 degrees F (0 degrees C) and turns off the heater.

Heating the coils every six hours takes energy, and it also cycles the food in the freezer through temperature changes. Most large chest freezers therefore require manual defrosting instead—the food lasts longer and the freezer uses less power.

It’s a refrigerator/freezer combo with refrigerator on top and freezer on the bottom, and it’s supposed to be “frost-free”. I understood that there were defrosting cycles, but I did not know about the heating coils. Thank you, @Judi.

Your welcome @2davidc8

Warranty? call them anyway.