add numbers to my account?

how do i add the other 2 numbers under my account?

I tried setting up my "account security" following the support guide, but i dont ahve such option.  I would like to pay my account bills all at once rather than login in to the 3 different account numbers.

For example, when i login, I get:

• Your phone number: (786) xxx-xxxx
• Lines on your account: 1

I would like it to say 3 instead.

Thanks