my refrigerator samsung is still not working properly

i have a refrigerator samsung, and the freezer is cooling to high that all my food gets like rock…and my fridge doesnt cool enough, its to low and all my food is being trown out…every other day we have to clean all the ice that built ups behind the panel…i also was suggested by one of the experts to change the defrost thermostat , which i did , it was working good for a 5 days and then it went bad…again…any other suggestions that my be wrong with the refrigerator…need help…as soon as possible…thank you