Last month, there was a $9.99 charge on my cell phone bill for something called "Chalk Board Quiz Club." I obviously would not have signed up for something like this. So I called AT&T, and the very nice lady who helped me said that companies send these little text messages out to cell phones, and they usually say something like, "Want cash? Text "yes" for more or "no" to stop." And if you respond back in any way (even if it's 'no') that tells these companies that you have a valid number and they will continue to send these texts and charge you for them. I get those annoying texts all the time, and I do remember one time responding "no" thinking it might make them stop. The lady said she would remove the charge and put a blocker on my line that would make it require my approval for any more charges like this.
I just wanted to share my story. It was so nice to deal with a customer service rep who was so friendly and helpful! I wish I would have caught her name.