MTN removes contractual services 500MB free/month

In December 2013 I subscribed to an MTN package inclusive of 500MB free data per month. This add was ongoing for about a month as one of the Christmas season specials for MTN. I signed a contract with MTN which included this 500 MB free data per month. I have during the last five months realised that my data usage was extraordinary high. Upon visiting my nearest MTN branch on 25 Nov 2014, I was dually informed that MTN decided to cease this said contract's 500 MB free a month, since the end of April 2014. I was never consulted on this matter and I feel this is a great injustice to its subscribers and users like myself. My feeling is that all users specifically chose this contract/cell phone package as it was advertised and was a GREAT deal. Now after contractually being committed after deciding on a cell package due to this specific adverti*****t, MTN broke the agreed-to contract by unilaterally stopping paid for- and contractually binded-to services, i.e., my 500 MB a month free data. MTN resolved it a week after the first report. On 30 Jan 2015 MTN again stopped my Data. Two calls to service desk, no update received. I again now do not have my 500MB a month. What is going on MTN?