Blocked numbers still able to text me

I’m having problems with texts from people I don’t know, unwanted messages. To block them, I have to put the number in my contacts and then block it. Tonight they are still able to text me! I’m so tired of this! Why can’ti block the text without having to keep the number as one of my contacts? And what is with the people who send out these texts, it looks like they send them to 20 or more people at once. Like anyone would really click on that? What can I do to stop this?