My sim card isnt working

[AC Question]

So when i first got my lg phone the sim card worked for about a day then it said invalid sim card. I had straight talk and they sent me a new sim card and that did the same thing. The third sim card they gave me was already activated. They said they would send me a new phone but never did. HOw would i explain this situation now, because when i asked them for a new phone it was when the 3rd sim card was already activate, so it would be kinda weird just saying give me a new phone. even if i bring up what happen. would they even believe me.