Mtn selling a lie

MTN sold me a lie. 3 months ago I bought a prepaid starter pack that includes 100% bonus airtime everytime I recharge, valid for 24 hours. The bonus airtime doesn't work. It slowly disappears in the course of the day. I have called the customer service centre countless times and everytime a different consultant tells me the issue has been resolved, but its never been resolved.

I believe this constitutes to false/misleading advertising and that MTN should be held accountable, or should actually cancel the bonus airtime as it is non existent