Response to "Smartphone dream turns into nightmare"

Please see below my Cell C complaint on Hello Peter. 10:25 Mon 21 Jul
To whom it may concern,

I always use this medium as a last resort but I am a little frustrated with my case logged initially in April, once in May, twice in June and now twice in July.

I opened a contract with Cell C in January (Iphone 5s, 16 GB, 100 Minutes, 100MB + 900MB additional data). 
Since I have had the contract (around 6 months now) my contract was loaded with only 300MB of data every month. I have paid for additional data every month over and above this 300MB. I have logged multiple queries regarding this but have still not received any feedback from the technical department. Every month I am billed almost twice the amount of what my contract should be.

I am almost at my contract limit for this month due to this error as well. I have also resorted to buying additional data bundles to compensate for the data I am not receiving so that the new out of bundle data does not let my account get out of hand. My line has been blocked due to the error on multiple occasions causing much frustration.

I see my account has still not been rectified as of today.
I would like to cancel my contract as I do not have faith in Cell C to correct this error (it has been over 4 months now)
Thank you for notifying us of the above.
We will ensure that this matter is rectified and hopefully we will be able restore your faith in Cell C. Apologies for the inconvenience caused.

Do expect communication during the course of the day.

Cell C | PN
My feedback:
I have not received any call from the department handling my refund. I had to call in today again. From what the consultant told me (who was very friendly and ready to help) and from what I understand, is that my account has been credited. However... It seems as if Cell C are netting off the refund against my usage in JUNE which is still not correct as the correct bundle was only added in JULY (this month). Will the refund from June net off against my usage in July? Not a happy chappy.
As you can see I have struggled and have been billed erroneously for over 5 months now. Am I entitled to cancel my contract as well as get refunded for the months I overpaid them?