Should I sue at&t for this or take another course of action?

Ok if you've read my other questions regarding suing at&t for this then you will know what I'm talking about. If not here's a summary, on Nov 7 I lost my cell I didn't know I had to report so I went on with the umption that it was gone for good My father officially canceled it on dec 10. On Jan 24 I received a call for 1000 dollars in charges for calls to made to El Salvador. I disputed the charges but since I didn't report it lost or stolen it was a hopeless cause. I eventually filed several complaints with the bbb and got a response from an executive specialist who told me they will not drop the charges. She did however give me one interesting bit of detail: a rate plan change made for my cell phone on Nov 11. I talked to my father and learned he suspended and canceled the phone on that date but at&t instead changed his plan instead of canceling it. My father eventually learned the phones were still active and officially canceled them on Dec 10. The executive specialist confirmed the Cancellation request on Nov 11 but claimed my father was persuaded not to cancel but just change his plan which I believe is BULL!!! I now believe they are trying to cover their es as I just recently received a phone call from the executive specialist saying they would take half instead of the full charges. However I don't agree as the phone calls to El Salvador started on Nov 11 the same day my father called in to cancel the phone. Now I'm wondering what would be the best course of action to take: Accept the half charges( if they still offer it) , sue to drop all charges entirely, or sue them in general?