AT&T Landline Billing Error. Need Escalation. Unresolved for over 12 months + 3 collection agencies

I would like to speak with someone who has authority and can honestly escalate/ resolve this situation. 

I am a longtime AT&T customer but I will not acquiesce to customer bully billing.

I am being charged for a landline phone that was never installed rather a U-Verse phone was but I was still billed for a landline phone. 

For over 12 months I have called several times explaining my situation with calls usually lasting 30-60+ minutes being sent to several departments and being assured this issue was resolved. 

In addition, I've been sent to 3 successive collection agencies trying to collect. 

I need this to be justly and immediately resolved. 

My faith in AT&T is waning.