You could forward the texts to SPAM (7726) and respond to the reply text you receive from Verizon. Or you can subscribe to Usage Controls ($4.99 per month). If it's a 10-digit number, you can block it free of charge via your on-line MyVerizon account.
Log in to My Verizon and use the free blocking option that allows you to block up to 5 phone numbers. If it is spam though they may very well just switch up the phone number they use to contact you. You can also opt to subscribe to the Usage Controls feature that costs (I believe) $4.99/month. You can read about the feature and all that it does on the VZW website.