British Airways refuses to honor return ticket.

I had purchased a round trip ticket for to and from Lusaka, Zambia between Chicago,US. I used to portion for Lusaka to Chicago in February 2008 and was due to return to Lusaka in June,2008. However, before June my hypertension worsen and I received medical attention thru September, 2008. Before June, we called British Airways to reschedule the return date and explain the situation. Because at that time , I could not provide a certain return date, I was told to call back when I knew when I would be able to travel.

When I called BA two weeks, I was tossed from rep to rep and asked to to call after 72 hrs, then 48 hrs another 48 hrs then 24 hrs. In all I made 9 calls in which I had to explain from the beginning each time. I was told to wait for the rates dept to review the case then was asked to provide personal medical records then finally was informed by a uncourteous supervisor number 2A in Jacksonville FL that the ticket was invalid. my ref was 43BCJV.

I would like to know how I can seek redress.