Why did I suddenly receive a text message? A relative borrowed money online, but sent me a reminder message. I told him I didn't know.

This thing actually filled in your phone number when your relatives borrowed online. You won't be notified if you fill in this, or there is your contact number in his address book, which is commonly known as address book explosion. You can only turn off the SMS function, and then only connect your phone to your contacts. It's annoying. It's no use calling the police. I have experienced it personally, and I hope it will help you.