Iphone sent for repairs

I have sent my Iphone - *** for repairs in feb 2015 an to date I have received no progress report nor have I got the phone back. Numerous attempts have been made and till now MTN has not gotten back with any feedback. Kindly advise the process for complaints as I am unsatisfied with the treatment I am receiving. I have two contracts with MTN and I would like to find out if this is the way MTN treats their loyal customers. My husband and daughter have Vodacom contracts past 10 year and have not had any problems with phone repairs and upgrades. If I don't have a response from MTN within two working days I am forced to cancel my contracts and port my numbers to Vodacom and I will never recommend MTN to any of our customers, friends and family.