What if i blacklist a contact who sends opt in purchaces for their service?

What if i blacklist a contact who sends opt in purchases for their service? This has happened to me twice in 2013. when I receive the txt it says Welcome to IFortune Daily Horoscopes ...... $9.99 a month. Type STOP to quit. If you don't type stop FAST! like seconds i mean.... you get a follow-up message that says congrats we just billed you 9.99! or like that and I called to cancel it worked out fine.

Then again the next time it said like "AT&T free message" Your subscription purchase was successful iFortune horoscopes and more for $10.99 will automatically renew on xx/xx/xx also canceled successfully. my question is if I block these will i simply not see the message but be billed all the same?

Anyone?

Thanks!