When you call, who do you need to talk to, to get thimgs done?

Yes, my mother passed away on the 23rd of August.  I called that same day to cancel her service and was told by a representative that service would end at the end of the cycle but it was prepaid and we would not receive any further bills.  Well on the 16th of September, we received another bill.  I called and spoke with 5 different representatives who did nothing but give me the run around and told me that in the State of New Mexico you can't cancel service in the middle of billing cycle.  My mom is gone, how is she suppose to pay for a bill at the end of the cycle?  When we called on the 23rd, this information was not given to us or explained.  I was on phone almost 2 hours being transferred back and forth, and no one could help me.  Horrible customer service representatives. Now they told me that I need to go into an AT&T center with my moms death certificate and try and catch a manger who might be able to help.  I live out of Albuquerque and it is not convenient for me to do this.