Question about Carrier unlock pin

Hi, my name is Jack.

I am a previous AT&T customer, and I bought my HTC One from AT&T
Recently, my HTC One had the factory reset, so it ask me for the "SIM Network unlock pin"

Therefore, I requested a carrier unlock from AT&T two days ago, but the email sent back saying that my account is closed.  

I called the customer representative, and he asked me to wait for 6 months to activate my phone.

So how will this work? 

Do I need to buy a new AT&T SIM card to activate my phone? Or I just wait for 6 months and I can get my phone unlock?

The representative also talked about buying an unlock pin on AT&T website, but where it is ?

Thank you and have a great day!

Sincerely,

Jack