How are people I don't know have my number and texting me?

I have an Iphone 4 and a couple of days ago I got a text that said they were someone from my school. They said Hey this is *persons first and last name here* from *persons grade*. What's up? (:
I have the persons number that they said they were already on my phone with their name labeled and I'm POSITIVE it wasn't her. I know for a fact she would have told me if she changed her number.
And today I got another text from a number I don't know. It said:
Hey!(:
~SINGLE~
I don't know who that is and I'm sort of getting creeped out, especially with the ~single~ label…
Does this happen a lot to anyone else? Because I've had a lot of phones and this has never happened until now and I want it to stop…

Sorry for so long of an explanation… But please help i'm getting annoyed by this

all answers are appreciated.

Someone could've put it as graffiti somewhere or used it as a fake phon number. It could also be a malware app that is faking messages or gave your phone info to an advertiser.

Lately I've been getting these text messages from people who I don't know. Just today one text said "this is how my sister got help when she needed it " Like WTF is someone spying on me? The other text messages are trying to get me to hit on some unknown sites for prizes or to sell me something!

  • Some number I don't know keeps calling me It's really scary. He calls like 2 times everyday… And I'm too afraid to pick it up. :/ The number is 650-419-5537. Can someone please call him… And like tell him to leave me alone. Or… How can I block him on my iPhone
  • People that buy iphones don't know anything about technology did you know that? Like my friend just brought iphone and I asked him if it has 4g late he said what's that? Then I asked how fast is the processor like 1.2 dual people buy them because its more mainstream and because their friends have iPhones Samsung is way better based on specs and technology the iPhone 4s and 4 processors are very slow
  • People keep calling me and I don't know who they are? I have a iphone 4 and I keep getting calls from people saying that I called them first, and I know didn't, their numbers aren't even in my recents. Today I got a call from a random saying to stop calling her and thought I was a telemarketer… How can I make this stop? And how did this even happen?
  • People I don't know appearing in iPhone 4s contacts? I have an iPhone 4s, and I just looked in my contacts and found a bunch of contacts that I've never added. It shows their names and numbers, and I don't know any of these people. Does someone else have their contacts connected to mine somehow? I don't use iCloud, by the way.