My money is no longer good

After being with mtn for the last 16 years, I now have trouble upgrading my device. I made an online upgrade application 2 weeks ago so that by Christmas my kids would get their new devices. I called in 3 times already and 2 out of the 3 times I was promised a call back and to my surprise didn't receive any. Like I previously stated I've been a loyal customer for over a decade. I expect better customer service than I'm receiving. Christmas is less than a week away and because of MTN, I'm stuck in a pickle. MTN please respond with a solution unless my money is no longer good for you