Samsung horrible at repairs

In December 2014 I received a Galaxy S5 brand new - sealed unit. Due to holidays/ travel arrangements, I only began using the phone later in the month. The phone hangs, heats up and regularly reboots. The phone was then given to Gijima AST, who is a client of MTN and MTN then in turn sent it to Samsung. Samsung replaced the battery and returned the phone just over two weeks later. The phone does exactly the same thing now, in fact it is getting worst. It hangs during calls and messages, when browsing etc!! I am a loyal customer of Samsung from the Galaxy S1 and am so terribly disappointed. Samsung are you that cheap that you cannot replace 1 single unit! Why should I end up with a faulty unit that cannot be repaired! I will send this phone through the second time for repairs and bear the losses (data to re-install everything and time without a unit I paid for!!), but after this you will never receive my business and I will endeavour to sway the decision of prospective buyers to Apple!