If not, then likely there is some residual value. Who were "the people at the terminal" who told you to call and rebook your trip when you sorted out your medical issue? If it was an AA agent, did they cancel your flight for you? If that's the case you may have some trip credit available to you. Unfortunately, that's for a future flight and not a refund.
if OP didnt have basic econ ticket, the agent shouldnt cancel the return ticket, but rather change it and charge OP the fare difference?