MTN - and not just data contracts - all phone contracts.
I was on a MTN AnyTime 500, that was discounted.
At the end of the 24 months, they removed the monthly discount and
reverted to a R500/pm "monthly contract".
I was not informed and only found out when I got my bill.
At the end of the term I had R2,500 accumulated in my account as AnyTime 500 was more than I used.
I asked if I could get a refund for the R2,500 - NO.
I asked if I could go stop paying for a few months (payment holiday) to use up the R2,500 - NO
I asked if I could transfer the R2,500 to another account - NO
I could only use the R2,500 by making lots of calls/sms/data and paying them R500pm.
I eventually gave up on the R2,500 and MTN and notified them that I would be porting to Cell-C.
When Cell-C requested the number, they were denied as I was on a "Monthly Contract".
I had to convert to a PAYG, then converted to Cell-C.
MTN are a bunch of crooks with shady practices - see "Former MTN exec admits to bribing Iran ambassador"
http://mybroadband.co.za/news/business/51659-former-mtn-exec-admits-to-bribing-iran-ambassador.html