Strange things happening on my iphone?

I bought a second-hand unlocked iphone yesterday, put my sim in, my contacts uploaded fine - but all day today, I've been receiving copies of text messages between the previous owner and the person he's been texting - its really strange!
… How can I stop receiving his messages?

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  • Why is this happening to my iPhone 5s? Sometimes when I'm in the messaging tap it will freeze. It will stay like that for about a min then continue to work like it did. This only happens while in my messaging tab. Why could this be happening?
  • Why are alerts not happening for calendar events in my iPhone. Alert is set for Time of event - yet there are never happening? Why are alerts not happening for calendar events in my iPhone. Alert is set for "Time of event" - yet there are never happening?
  • What's happening to my iphone? TECHY PEOPLE Please Help. My white iphone 4s has been acting so freaking weird, first the sound stopped working without headphones then it didn't even work with headphones! The battery died and i went to charge it, it began to start up but then the screen went white and then black. It did that so many times on its won without me even touching it. Can someone please tell me what's going on? I'm so mad right now. Its not jailbroken
  • What's happening to my iPhone and his? So I set up my own account on iTunes synced it to my laptop, and my dads friend ask me of I could do his, that was fine set it up in HIS own account. So mine and his are different BUT he keeps some of my texts and gets all the new apps I download and music. He said to my dad he doesn't know half the stuff going on with his phone he just goes with the flow. But how come he's getting some of my messages? That's weird I don't want him knowing what I'm sending -.