That happens to me quite often, on SN, LH and few other flights.

The remedy however is easy: read carefully what they write in this auto-response:
If you disagree with this decision pls send in copy of flight ticket or e-ticket receipt to our Retro Department, [email protected] , together with this reply.

I have emailed this many times and in usually 1 week it is done (if the booking class is eligible, of course).