MTN are *****ulent

I took a contract with MTN and the person who assisted me made a ***** on my account, i told him that to link my phone with the previous contract i had and i told him that my spend limit is 0 but instead he choose to make my spend limit to R1700 some change, how can you take a contract of R500 because you afford R500 than MTN decide to make extra contract without your approval and they don't tell all this you saw it when you receive statement, now i must so much without being acknowledged, because when you take a R500 contract it because you afford that R500. So i feel that they are doing *****ulent to me, i will open a case for them.