Ridiculous OOB charges on Top-up contract!!!

I was very shocked to get my Oct bill with the extra R145.16 data charges and this morning my Nov bill with extra R106.22 data charges. My contract rate is R259 with a usual payment of between R200/R220 - shot up to R401.97 for Oct and R322 for Nov. But for the past 2 months, I use Wi-Fi during the day, only using my contract data during the evening between 7-11 - so logically should be using LESS data?!!!<br> The reason I am so very shocked is that I have a TOPUP contract with MTN!!! Meaning that once the data and airtime received a/p my contract is depleted, I personally have to topup my account with airtime for data.<br> How is it possible that I am charged out of bundle rates (only for the past 2 months) when I have a Topup account?!!!<br> MTN state that I have an OPEN ACCOUNT with a R200 limit set which after I reach it, I am charged these rates?! And if I don't want this option (WHICH I NEVER CHOSE AS I HAVE A TOPUP CONTRACT) I have to go to an MTN store and set the limit to R0.<br> How did I suddenly get a R200 limit (WHICH I DID NOT ASK FOR) giving MTN permission to charge OOB rates once reached a year into my TOPUP contract?! <br> <br> And they just shrug their shoulders at the call-centre...