Call customer service at 1-800-922-0204 from a landline or another cellular phone at *611 to cancel the line. You can also visit a corporate store to cancel. Be polite but firm when talking to the agent as they will attempt to get you to stay. Don't let them suspend the line.
You can't cancel online because they need to verify your identity before processing the cancelation.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.