How can I know this is the right number? (Score 1)

Is this letter from Verizon Wireless, or from a phisher? Is the phone number real? I called up Verizon Wirelss (using 611 from my phone -- not at the number on the letter) but they were unwilling to confirm or deny that they are doing this, or that 800-333-9956 is the correct phone number to opt out. After a few tries, I was able to explain to the customer service representative that anyone can send out letters claiming that they're Verizon, telling people to call and provide their SSNs. She agreed to file a complaint that will be reviewed by their marketing department. She noted in my complaint that I have no intention of doing any further business with Verizon Wireless, as a result of this stunt.