Same thing here, i was on Vodacom the last 15 days and bundle ran out . I wanted to buy a 1GB MTN bundle this time around, so now it's still R399 vs. R289 at Vodacom.
The thing that broke the camel's back though was, even though my Vodacom bundle ran out before the 30 days, I COULD BUY A NEW BUNDLE IMMEDIATELY regardless of the expiry date of the "existing" bundle. The moment i buy a new bundle i get a new expiry date 30 days from the date of new bundle activation...
On MTN the steps are as follows:
Buy 1GB -> expiry 30 days later.
You use up 1GB in 20 days
Now you need to swop sims and load 1GB on the new sim
..and repeat
Methinks MTN needs to adjust a few things very quickly.