I'm one of those who also had major issues. They decided to just remove all my saved up data and change my contract. Obviously, they then also decided to bill me for data usage that they shouldn't have charged.
I initially mentioned some issues I had
in this thread. I have contacted Minette and got a call back as mentioned there, but no follow up yet regarding my data issue. I've also mailed "the CEO" (address is given with bill statement), but to no avail.
At the end of March, I requested a data available summary and got this:

Quite a bit of data to use in April and May.
Now, after I was moved from Autopage to Glocell I got a message that said one of my bundles expired. I was on holiday (away from any wifi) and downloaded a few apps after I factory reset my phone. My estimate was ~1.5 - 1.7GB for the month. This was not of big concern as I knew (thought) I still had quite a bit left. When I tried to get a new balance statement, just said I had 0 mb left, but no option to send a detailed SMS stating this. I thought this was just a bug, so I mailed GloCell and never had a response.
Now, over the weekend, I received my April bill (for some reason only the summary and not my itemised bill was sent) and got quite the shock:

The highlighted portion shows that I'm still supposed to receive my 1 GB data per month (I signed up initially with a Autopage special StraightUp 100 with 1 GB data / month). Something that clearly never happened.
Now, for the next surprise... On the 9th of May I submitted my request for contract termination and was informed by the call centre agent (Shannon?) that it would take 30 days till cancellation. On the evening of the 13th I'm standing outside my friend's gate and try to call him to open up (intercom is broken), but I just get a recorded message "If you are on prepaid, please recharge airtime" and then a bunch of SMSes from CellC to welcome me to EasyChat prepaid (at this point I'm very glad that the Capitec app is zero rated).
At least now I can port to Vodacom and for once in 2 years have decent cell reception again - I really don't understand how CellC can claim they have the widest network coverage - have they been to PTA, JHB, the karoo or CPT any time recently?