Do you have unified billing? (Combined Uverse, direct tv and wireless for a discount). If so, this has been a problem for many customers in paying off Next or upgrading phones. If this is the problem, de-combine/un-unify your accounts to regain control of the wireless account. It can take 2 weeks.
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1. ONE person....Only one person should have access. It isn't a matter of trust, but of organization.
2. Records. I don't know about you, but I have far too many accounts, passwords, security questions to remember it all. I use a password app, synced through Dropbox to all my electronics. I only have to remember the one password to access all my records.
3. Email, as in secure yours. If someone hacks your email it's easy to reset passwords and access your accounts.
4. A little paranoia. I change the 4 digit pin every time I use it in a store. I'm asked to give the number and I don't know who is listening or how carefully my account is guarded. I've changed it 3 times this year because all my lines are upgrade eligible.
Without the PIN nobody should have access to even question your account balance. Going in to prove your identity is a nuisance, but at least your account is secure.
Your online bill may not show adjustments. Once a bill is posted, it can't be changed, you would have to call to know what adjustments are pending. But it should allow you to upgrade, unless the idiocy we call unified billing is messing up the works.