Originally Posted by WineCountryUA

That;s the problem. You used FFC as the starting point and rebooked the same flight and therefore maintained the original PNR. No residual in that case.

If you had changed to a different flight, did another cancel and then rebooked the original flight - keeps the original PNR but then the residual FFC is generated
or (my preference)
you do a new booking (ignoring the FFC) and then at the end apply the FFC as a form of payment This creates a new PNR and a residual (original) FFC

From the thread's wiki