MTN not honouring the package that was promised when renewing the contract

I renewed 4 of my contracts with MTN and was told that i would get 500 minutes and 15gigs of data every month for the duration of my contract. MTN stopped giving the 500 minutes and i have made numerous calls to MTN and they are really unable to assist me. I keep being transferred from one department to another and it seems like they have no clue what to do. This is so frustrating and so unfair on the way the customers are being dealt with