Bundle price changes without notification

How the hell can data bundles just be changed without notification, i have bought the 7 day 5gig for R49 3-5 times a week for the past 4months, now all of a sudden its R100 for 5gigs for 7days( 50% off) What s... is this, i would rather then use my FNB and earn ebucks and better prices than this, also ill pay up my contract and move to another sp. I have been with mtn since 2000, but for the amount i spend on my PAYG sim, to be blindsided like this, does not work. Its really ****y business practices