How to stop unwanted texts from random business?

I don't know how they got my # b/c I NEVER give my cell phone number out for exactly this reason but I keep getting texts from telemarketers, I have a very limited # of texts a month and I would prefer to be able to use them for tlking with my friends not learning about how I can turn $96 into $96000. I'm on the national do not call list already, is there a national do not text list that anyone knows about.