Why no cancellation confirmation?

An email is normally received within 24 months at the latest. I would call back and verify that account was set to be canceled, and that the contact email on file is correct. You can also post back with the model numbers of your boxes to get guidance on if they are required to be returned.

Also be aware, cancellation doesn't go through until the end of the service month. They stopped prorating bills a while back. Here is the notice from 2018.

Please read this if you receive DIRECTV, AT&T U-verse® TV, AT&T Internet, AT&T Phone, and/or AT&T Fixed Wireless service(s). We want to remind you that you’re billed in advance for recurring service(s) and/or programming charges and applicable fees based on the terms of your current service agreement(s) with us. Starting January 14, 2019, subject to applicable laws, we’re updating your agreement(s) to include your recurring service(s)/programming charges and fees won’t be prorated if you cancel the above service(s) on any day other than the last day of your billing cycle. Your service(s) will continue until the end of your billing cycle but you won’t get a refund (prorated credits) for any remaining days left in your billing cycle. For products not listed above, refer to their terms of service for more information.

Questions about this change? Go to att.com/ProrationPolicy for more information and to see the revised section of your service agreement(s).