"Cancel e-ticket" option can be used only upto chart preparation. "File TDR" is used to get refund after preparation of chart for confirmed/RAC tickets if they have been unused.
According to me, the only exception when "cancel e-ticket" option can be used after preparation of chart is in case the train is marked as "CANCELLED" in PRS due to breaches, floods, accidents etc.
e-Ticket can be cancelled within three days of the scheduled departure of the train.