Another way to turn it off is to switch from the $2.99/month Premium Visual Voicemail to regular iPhone Voicemail, which doesn't offer voicemail to text message as a feature. Again, you do that (on a PC browser) by going to verizonwireless dot com, log in to your account, hover the mouse over "My Verizon" at the top, hover over "My plans and services" below that, then click on "Manage Products and Apps". From there you can change your voicemail settings.
Or you can probably call Verizon support and ask them to turn the feature off for you.