Service turning me off

My daughter's phone is under warranty and we took it back to CNA who sent it to Samsung for repairs, because it switches off by itself constantly. After two weeks, we got it back today. All they did was replace the battery, but they never bothered to test it. It's still doing the exact same thing. What gives? I've always been a huge Samsung fan, and all our phones are Samsungs, and we have plans on buying two more in the near future, but I've got to know that if I spend money, I will get the service I deserve as a loyal customer.