SAA downgrading clients and no customer relations even respond

Last year we booked a return business class tkt overseas with SAA. SAA downgraded my husband from business class to economy on the last leg of his journey. In february this year we contacted their customer relations, to which they responded saying they were investigating and would respond within 10 days. It is now 2 months, and there is still not even an acknowledgement or response from SAA. He purchased a business class ticket and flew economy. Surely SAA would have the decency to respond to a business class passenger. We have now emailed them about 15 times....... but they do not have the decency to even respond.