What would cause your 3 yr old bottom freezer refrigerator to keep having ice on the bottom of the freezer?

The most likely cause is that the defroster drain is clogged with ice.

During the defrost cycle, a small heater warms the evaporator coils, allowing accumulated ice to melt. The water is then collected in a drain, where it drips into a pan underneath the refrigerator, and evaporates.

If the meltwater re-freezes in the drain, then during the next defrost cycle, more water will back up and freeze, clogging it further. Eventually, the water will overflow into the freezer compartment, resulting in this condition.

If this is the cause, the simplest way to fix this is simply to pack all your food in a cooler with dry ice, and then unplug the refrigerator for about six hours. This will let all the ice in the defroster drain melt out. Put lots of towels around the bottom if you don't want a mess.

If you are up for a fix-it adventure, another solution is to unplug the refrigerator, and remove the panels inside the refrigerator, then put a small immersion heater in the defrost drain area until it is clear. This way you may be able to avoid removing all the food.