SAMSUNG S5 MINI - FAULTY

I have two Samsung S5 Mini cell phones bought at the same time from the same shop in December 2014. Both phones have the same problems! I have sent the one phone in to the advanced repair center 3 times. First two times they told me there was no problem with the phone! Third time I took the phone in while it was displaying the problem so they replaced a whole bunch of stuff. Low and behold the phone still has problems!!! I am so sick of these two phones its not even funny!!!