Samsung Galaxy s5 mini cellular device no signal

I purchased a Samsung Galaxy s5 Mini in October 2014. The cellular device worked for a short period of time. After a couple of months the device started to experience signal problems. The phone loses signal or it keeps showing alerts that it is not registered on a network. I had to set the phone to the basic network setting to have network access. I took the phone to the Samsung care centre in the rodepoort area. The first time they reinstalled the software. After a couple of days the phone started giving problems again. I took the phone back so that they can do test and fix the problem. The first time the assistant told me that if the phone starts to give problems again it is most probably the hardware. The second time I told the employee about what happened the first to me and what they told me. They said they will fix it. The day I received the phone back they just reinstalled the software again. They did a signal test and showed it worked again. After 4h after the phone being switched on the signal problems started again. It shows that the device has signal but the data icon is off and no one can contact me on my cellular device or sent anything from the device