I need contact address to send complaint letter

I need an address to send a complaint letter.  I paid for the same service twice last year. I renewed my subscription April, 2016 but they kept sending me messages that my computer was not protected so I bought a subscription again in November.  I am old and tend to forget stuff.  I did the live chat, Lyzajenn canceled Norton 360 but did not credit my account for the 3 years I paid for.  I want to send BBB and the main office a letter regarding this matter.