Want to retain Airtime on signing new contract

Canal Walk store advised that Retentions dept can give a reference to credit me with almost R600 airtime, on signing a new Top-UP contract. Since 17/08/2015 I am struggling with call centre and emails to Retentions Escalations and Customer Care . Every time I get promised that someone will contact me. NOBODY has called me. I have made many calls, but no response. At first I was told within 2 to4 hours, then 24 hours and the next time 7 working days for someone to get back to me. Now, 3 weeks later and still no reply. Apparently the Retentions dept does not take calls as they have a \back-log". After 17 years of having a contract with MTN"