How are you supposed to contact AT&T to order a new router?

The 3600 HGV router that I purchased from AT&T way back when stopped broadcasting after 7 years or so.

• Green 'wireless' LED is the only light which is off.
• WiFi AP not visible from any device.
• I've tried a power cycle and a factory reset.

I'd like to get a newer router, but can't find any way to contact AT&T.

So now I'm asking the community. Could anyone please tell me how to contact the right people to initiate a router upgrade?