My cousin does not want to pay his bill that I added him to my line so how can I remove him from line without him knowing ?
That's unfortunate your cousin is being a deadbeat on the phone bill. Since his line is on your account, you must be the Account Owner and are managing both your line and his line? I doubt that your cousin wouldn't know about his service being cut off, but since you are financially responsible for any bills on the line in question, see here:
https://www.verizon.com/support/disconnect-cancel-mobile/
