BLACK FRIDAY DATA DEAL INCREASE FROM R349 TO R429 - 12%

So my MTN BLACK FRIDAY data contract for R349 has been increase by 5% as of May 2022. My 2yr contract ends in Nov. So my new installment is R429. I am not sure how MTN got there. To me that's a 12% increase. So i logged a query *** and was closed today. After calling MTN for feedback, i was told it was correct. Pls explain how this is so?