Why does my mobile phone receive messages from others?

If you bought your mobile phone in a mobile phone store and someone else set it up for you, and you didn't add your own apple ID, then you used someone else's ID number. In other words, all people who buy mobile phones in his store may use this ID number, so Apple's FACE TIME and IMESSAGE can be received as long as they use this ID, and if you don't play with Apple's settings, people can locate yours, that is, he can know where all mobile phone users who use his ID are.

Set-Privacy-Location Service (off), Information-Imessage (off) and FaceTime (off) first, so that you can only receive the information of your mobile phone number.

Apply for an apple ID and change it to your own. Apple's settings are actually reasonable, you will know after playing.