Trade In Discount ****

I went to MTN Menlyn on the 24th of February 2024 to do a trade in for my old device for a new phone. I was supposed to receive a R400 Discount on my contract monthly value but even today MTN is deducting the full amount claiming that my trade in was not app****. The store showed me all emails and communications with their headquarters but I am still billed for the full value.

Imagine my old device has been with MTN for 3 months now but I'm still not benefiting anything, why was there a need to trade in my device if I won't be benefiting? This MTN trade in thing is a ****!