Ignorance of MTN.

Since I upgraded my MTN Contract on 26 January 2021. My spend/Usage limit was taken away. The Shop where the upgrade took place allege that I should phone 135 and the spend/usage limit will be added again. After 9 calls to 135, spoken to various different people, the spent/usage limit is still not sorted out. I received two SMS Messages where MTN closed the matter but it is still not sorted. What can be done to settle this matter.