Samsung Repair Centre Roodepoort

I handed in my Samsung Galaxy S5 mini for repairs in December 2014, since then I took the phone back another two times and it seems that I need to take it back for a fourth time now as I am having endless problems since they repaired the phone. I upgraded on 14/09/2014 meaning that my phone was brand new. First repair free, second repair paid around R900.00, third repair paid for back-up around R250.00. On collection only was I informed that they have replaced the mainboard, I wasn't charged nor was I given an explanation as to why they needed to replace it, but the fact that it was done for free! Is it because of their negligence? and if so, why was it not replaced? another week down the line and it started giving me problems AGAIN, took long to register when doing anything or using apps and then all of a sudden emergency calls only. I did check the sim, removed the battery and tried everything - no service...by this time I'm so fed up with my phone and it looks nothing like before. its full of repair stickers and sticky all over. I send e-mails to three different people without any reply as jet. I need to use my phone, paying it but have no use, not on!!!!