Contact your cell carrier and report the number as a nuisance number and request it be blocked. Inquire if they offer a service to black list numbers so they can not call or message you at all, Verizon lets you block up to 5 for free.
Also inquire if you can forward the text to 7726 aka SPAM:
http://www.fcc.gov/guides/spam-unwanted-text-messages-and-email
"Do not respond to unwanted texts or emails from questionable sources. Several mobile service providers will allow you to forward unwanted spam texts by simply texting it to 7726 (or “SPAM”) to enable the providers to prevent future unwanted texts from the specific sender. "

If you have a smart phone, there are many anti-spam apps. Check your phone's app store.