Final billing frustration

After nearly 40 years with AT&T I finally cancelled my service, went with another carrier, and requested a final paper invoice to verify my ending balance.  Two months later I have yet to receive such.  I have logged my many phone calls, now totaling over 5 hours and with as many different run-arounds.  The other day I received a past due notice for the balance on my last phone purchased but when I call and request a breakdown of the final bill (nearly 40.00 more than previous months) I am told my account be located.  Wednesday I was told I did NOT owe any final charges (I wish, but know this is incorrect).  When I requested an email be sent me stating such, I of course did not receive it either. I have been disconnected, transferred to "never never land", lied to, apologized to (from what sounds like scripted text) but am still without a bill or an explanation of charges.  When I call and request a supervisor I sit on hold up to 30 minutes and then disconnect.  Any suggestions?