How can I get to a live agent?

Another option is to take a copy of the Death Certificate into a CORPORATE Store.

We're here to help you, paccorinti.

We're sorry to hear about your son. In order to cancel this account, you'll have to call AT&T directly at #800.288.2020 then follow the prompts to reach the loyalty department.

Thank you for choosing AT&T.

Yomi, AT&T Community Specialist

I spent almost 2 hours on hold until I finally reached a live person. He was very kind and tried to help me but he said he had to transfer me to another agent that could actually close the account. He told me he would stay on the call until he could transfer me. When he was ready to transfer me, he told me the name of the person I would be talking to and then click, nothing. I lost the connection. I tried to call back, this was about 3:30pm and got as far as a recording telling me to call back during regular business hours. Totally crazy. 

what you can do on the bill there is a mailing address mail in the death certificate  with a ZERO marking and your contact into I run into the same issue with my family  member passaway about a year ago  on the billing sub include your name and phone number at least for me someone called me to confirm  that was the only way I was able to close the account 
if that's to complex follow

Change a Wireless Account Due to a Life Event - AT&T Wireless Customer Support (att.com)