Promotional services billed without my approval

I entered into a 24 month contract in July 2016. The contract was on promotion with an additional 2GB data and 200 MTN-to-MTN minutes for the first 12 months. So I was billed R349 each month until August 2017. Then I get slapped with a massive debit order of R769 (despite having set a R50 limit on out-of-bundle usage).

So first I send a DM on Twitter to @MTNza asking who I could contact about billing issues on 2 September 2017. I have not received any reply to date (more than 2 weeks later). Then I log into MTN Active on the website and log a query (ref no ********** 31) on 5 September. Again I have not received any feedback on this query to date.

So eventually I went into the Tygervalley MTN store on 9 September to find out what was going on with my crazy high bill. The guy then tells me that promotional items automatically get charged to your account after the promotional period. I told him this is ******* since the contract that I signed does not say anything like that.

A promotional thing is supposed to end after a certain period. You can't simply start charging R420 extra per month on my bill for something I did not approve at any stage! What is the point then if me having set a R50 limit?? This is ***** and I demand a response from MTN (along with a refund).