Frost buildup in freezer, ice buildup on interior refrigerator wall and ice maker doesn’t work

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Brand:Samsung
Model Number:RFG237AARS
**Main Symptom:**Frost buildup in freezer, ice buildup on interior refrigerator wall and ice maker doesn’t work.
**What happens & when:**Frost buildup in freezer, ice buildup on interior refrigerator wall and ice maker doesn’t work.
What happens & when: After a repairman defrosted the unit, replaced the “main board” , the “Defrost thermostat” and “Temperature sensor” the unit worked fine. Over the next 3 months frost build up again and the icemaker stopped working. We called the company back but they said they only warranty repairs for 90 days so we were just over by a few days. With the $600 we had to pay for the service we are not able to call another company to come out. Can you please explain what may have happened or walk me through what else I should replace to get us up and running again. Any help is greatly appreciated.

Error Code (if any):none
Parts or tests already tried: see above
Photos / video link:I am including a picture of the frost in the freezer and ice buildup on the wall of the refrigerator.

Duplicate question, already answered.