freezer not cooling

Hi. Unfortunately it sounds like you have a sealed system problem. You should have light frost across the whole evaporator. A partial frost pattern or a ball of ice on the incoming side of the evaporator is a symptom for a sealed system issue. You could have a leak in the system, a restriction, or a faulty compressor. This is an expensive repair for a company to perform and usually is not cost effective. You would need to install access valves to tap the system and check your high and low pressures with a set of refrigerant gauges.