LG G3 Phone

Got new LG G3 phone last year September and I have to say this was the bigest mistake to go from Samsung to LG. I have never strugelled so much with a phone that I am with this phone. First of all I keep on loosing signal doesn't matter where I am. Secondly the phone keeps on diying when I am in a app like face book and my phone rings. Can't believe I have to struggel with such a bad Product. I first though it might be a problem with my sim card and already did 2 Sim swaps since I got it in September. Then I though it might have to do with the area that I am in on the Mtn network but I never had any problems before and mtn asured me there is nothing wrong with the towers.