Mtn picks who they upgrade

A week ago I realized my Mtn cellphone contract is due for an upgrade. I then call the call center and they say they will get back to me. Never got a call. Go to an Mtn branch and apply for the upgrade and the lady then states that she will contact me once the upgrade is approved. Still not contacted. I then go to the store again asking for the lady, she comes back saying my upgrade was declined because of my debt review. Which cannot be the case as my upgrade was within my credit limit. If I was not allowed an upgrade then Mtn should’ve stated this from the application. I need more information on this as I paid on time every month and I get such a disappointment.