Due to the snow-induced meltdown in IST on 18/FEB, I am now in the same situation as the OP. The one cancelled flight in question is the one making me Elite+, so I am quite keen on these miles.

The automated retro-claim form did not work for me, so I used the online contact form to request mileage credit. I've attached 1) boarding pass for cancelled flight 2) screen shot of cancellation 3) original ticket.

Will see how it goes...