iPad/iPhone Lock Screen displays messages from unknown senders . . .

Greetings wise, and knowledgeable countrymen! Question please. I greatly appreciate your kind help.

Issue: On my iPad, and iPhone I receive notification of text messages from unknown senders on my Lock Screen. I do not see the actual messages in the Messages App., as I only allow messages from numbers in my contacts. However, I cannot figure out how to prevent the unknown sender's messages from appearing on my lock screen.

I'm sure I'm missing something. Will someone please tell me how I can fix this?

I greatly appreciate your time, and expertise! It's always good to learn new information. In exchange, I can only offer the following senior observation. (Not sure this one counts as wisdom.)

In my experience, I have found that the old adage, "You can't teach an old dog new tricks," just ain't true! You can indeed teach us; however, there exists a disproportionate probability that you will have to teach us again tomorrow. Just my experience.

Cheers!