AT&T is particular is remarkably persistent with its marketing.
General instructions for AT&T customers for opting out can be found here:
https://www.att.com/support/article/wireless/KM1011260/
but I am not an AT&T customer.
This marketing series of phone calls was from their DirectTV department.
Go to: https://www.att.com/directv/
Click Chat on the right.
Make the subject: Opt out of marketing phone calls. (Or similar.)
The agent (which may or not be a person) will come on the line and will ask for your name (first name is ok.) It will ask if you use any AT&T services. (We don't).
Then it will ask for the phone number to remove.
With any luck you should see:
During the chat session you can request that a transcript of the call be either emailed or texted to you. This can be quite handy.
Your chat transcript:
PLEASE DO NOT REPLY TO THIS MESSAGE - All replies are automatically deleted.
AT&T : Thank you for choosing AT&T Chat. How can we assist you today?
Me : opt out of AT&T marketing phone calls
Emma : Hi! My name is Emma. I can help you by checking our internet options today.
Emma : I will be more than happy to check your internet options in your area.
Emma : Can I get your name?
Me : Ellen
Emma : Hi Ellen, Nice to chat with you.
Emma : While I'm checking this for you, can I know if you currently have any existing services with AT&T? (DirecTV, DirecTV Stream, internet, wireless)
Me : we are not AT&T customers
Emma : Thank you so much for that info
Emma : Can I get your phone number ?
Me : XXX-XXX-XXXX
Emma : Thank you , please allow me a few moment
Emma : Done, this is your confirmation number ##############
Emma : Your DO NOT CALL Suppression Request has been successfully submitted!
Emma : Your number will be added to our AT&T DO NOT CALL LIST.
Me : thank you.
Emma : My entire pleasure
Emma : I want to be sure I gave you the best service possible. Is there anything else you need help with today?
Me : no thank you, have a good day.
Emma : It was my entire pleasure to assist you today
Emma : Have a good day, thank you for contacting us today. We appreciate your business!