Moving from AT&T prepay to AT&T postpay

I went yesterday to an AT&T store to switch my prepay account to a postpay account (with my own phone).

The representative (and his manager), told me that since my SSN has the closure “Valid for work only” I will need to pay a $500 deposit (even though I have good credit score…)

The odd part, is that I need to pay the deposit only if I transfer the account. If I create a new postpay account (and in the process get a new phone number…), I can avoid the deposit. It does not makes sense (and the manager agreed with me...)

Can anyone help me or knows what needs to be done to resolve this?