faulty phone after repairs done

In October 2015 I took my phone to Samsung Smartcare Century City to have my cracked LCD fixed under warranty.I collected my phone two weeks later and was impressed at that time.Three weeks later my touchscreen and buttons on the phone was non functional.I took the phone back .When collecting my phome yet again i was informed that my motherboard was replaced.I found it difficult to understand as their was no apparent problem with the motherboard but with my LCD.Two weeks after collection I had no network coverage on my phone.Find myself back yet again at Smartcare only to discover that somehow my IMEI number was not registering on my motherboard.Their words was it disappeared from my motherboard.I was left without my phone for yet another couple of weeks.Now 5 months later i find my myself with the same situation,no network coverage.Before taking my phone back i need clarity.Why I ended up with all these non related problems with my phone .I initially took it for service to have my cracked LCD replaced.I am at the point of wanting to throw this phone in the bin.I have up until November ,then my warranty expires.What will happpen after that with all these problems im experiencing.