I have the same issue after I 'upgraded' my phone to a droid charge a few weeks ago but they are just texting me. I tried sending 1 text w/ 'stop' but it didn't work (it also doesn't even show up on my text log). I just blocked the # on verizon's website.
I am getting this same text. If you block it online it will charge you $4.99 a month. If you call Verizon tell them this is called "premium message" and ask them to block all premium messages. There is no fee for this. Do not reply back as it said it may charge you. You need to check you bill when it comes in to make sure you are not charged for any of this. If it is you have proof of calling Verizon about this problem. Ask the to set a follow up to review your bill after the billing date to make sure it is not on the bill.
Log on to My Verizonwireless. Click on Block Calls & Messages. Select Internet Spam Blocking, and check the boxes for "Block all text messages sent from the web" and "Block all text messages sent from email" then hit Apply. Finally, retart your phone. Hope it'll help!