Mtn staff unwilling and dont have knowledge

I'm busy with MTN for more than a month. They run a promotion where you get Data at a discounted prices. I top up on my bank and convert the airtime to Data. I purchased the 7 day data. It doesn't use the time base data - it keeps using my contract data and then my data expire. I send a mail to customer care. 1st they couldnt see that I purchase data then I draw it on my app and they can still hot explain. I phoned and the 1 lady said I must switch off my device it will work now. It didn't the next one say I can't buy data but she will come back to me because I insist on a refund and she never came back. The service is the worse ever received from a supplier. Looks like the staff don't care and don't have knowledge. I need someone willing with knowledge to assist