I put my phone number in a CL ad; no need to explain why one should not do this…
Some say “Text STOP to stop” but others have no such function.
By texting “stop”, you are telling the spammer that they have found a live number to spam. You can block individual numbers by blacklisting them or you can allow through only numbers you choose yourself with a “whitelisting” app. (Similar options are surely available for an iPhone, if that is what you have.)
I wouldn’t do that “text STOP” thing either. Verizon has some “report spam” option; I’ve been using that. Seems to be working!
you could try using an app called truecaller. I’ve used it for quite a while and it helps both with sms and calling! 
For texts originating from an email address, with no phone number: I blocked the phrase “subject:”, and I haven’t seen one since.
On an iPhone you can block callers:
In your Messages app:
- Tap on the spam text message
- At the top center of the text screen it shows the phone number (of it may show a business name) and in the top right it shows an “i” in a circle (for information). Tap the “i”
- You will see the “Details” of this caller. Tap the phone number or name of the caller.
- The next window is their “Contact Card”. Tap “Block this Caller”.
You won’t get any texts or calls from this number again.
If you go to your Contacts app, you will see these listed as “Blocked Caller 1” “Blocked Caller 2” etc.
BTW - This is a website I have used to try to figure out who exactly is calling / texting. http://800notes.com
I would recommend against TrueCaller. They have been known to make all the phone numbers they are provided public, and they upload all your contacts.
I don’t get spam text messages, but the Hiya app is very good at identifying and blocking spam phone calls. Might be worth checking out.