Very poor service from Mtn

Very disappointed with Mtn Mobile, upgraded contract which I have for more than 10 years in 09/01/2019 via a call from 1 of their service providers was told that I wud receive my handset within 5 (five) working days, to date(18/06/2019) I haven't yet received even a call from Mtn. I called various times and even spoke to senior managers who told me that they will escalate query to appropriate dept and will call me back within 24 hours but still nothing. My last call to them I spoke to a manager who even told me that he cc'd himself into mails from correct dept to myself and its now been 3 weeks. I further want to say that I have been billed monthly for this upgrade although I havent received wat was due to me. This is now the final straw. Hope to sort out this problem