Downgrade reimbursement can be claimed based on the Mennens formula for partial downgrades.

As the change to your ticket was involuntary, I believe you can be rebooked in a revenue class, award space need not be available. But of course, expect the call centre telling you to pound sand.
If you prefer to be rebooked, contact M&M as they issued the ticket. If you prefer downgrade reimbursement, contact SA as they are the operating carrier and also expect them to tell you to pound sand or to offer a laughable compensation as it is an award ticket.

If it's worth fighting for is your judgement. Either way, almost nothing to gain.