Data management on Internet Bundle

I purchase a 2Gb Wi Fi Internet Bundle from MTN each month, they give you an additional 2Gb promotional data \free\" and 1Gb Night Express \"free\". When you use the Internet normally they are supposed to take the usage off the promotional data first, when this is used up they revert to your Internet Bundle. This has not happened, they use up my Internet Bundle first which then forces me to purchase a new bundle.<br> There has been email between them and myself for the past eight weeks now and it does not get resolved. All they do is ***** your data. What a pathetic company."