How to terminate Bellsouth FastAccess DSL Xtreme 6.0 billing? Now have AT&T Internet Basic 6.

I am being billed for BellSouth FastAccess DSL Xtreme 6.0 and AT&T Internet Basic 6 simultaneoulsy. I only need one of them.

The BellSouth DSL account should have terminated when I began AT&T Internet Basic 6, yet billing shows both are active.

Who do I contact that can examine both accounts and adjust the billing?

Thank you.

By the way, here's what I've do so far in an attempt to address this:

On ATT live chat: I consulted Mack > he handed me off to Alisha.  She said ATT would call me. No one called.

Next Day: I spoke with LoAnn > she handed me off to > Kenny > Alex > LJ  who said I should call someone else.  I gave up after 50 minutes on the telephone (I had to get back to work) .

The problem remains unresolved.

Each person I speak to tells me that it's someone else's department.

Isn't anyone skilled enough to look at my account, terminate it, and fix a billing issue?