Greylisted on app, no assistance from MTN to correct

2 Phone was ****** on 16 Augustus. The Iphones was wiped and blocked. Did a sim swop at MTN on 17 Augustus to be block the sim cards. Upgraded on 19 August. One phone worked 100%. Other phone not sorted up to date. The MTN app does not open and indicate greylisted. Been to MTN shops 7 times and countless phone calls. MTN can not assist to remove the greylisting. Went to Menlyn Mane shop on Friday 8 September being told customer service does not really work on Friday, they will have a look on Monday. Why can’t MTN sort this issue??