Where do you go to complain about Nedbank's Complaints Department?

I left a message at the call centre for my relationship banker to phone me about a problem I had. She has never phoned. I sent an email to the relationship banker giving details of the query. She has not responded. I sent an email to the Complaints Department complaining about the poor service and requesting they resolve the problem. They have not responded.

Things are in a really bad way when you need to complain about the Complaints Department. Or perhaps they are so overwhelmed with the number of complaints regarding their non-existent service that they cannot cope with the volume.