Cell C account - disgraceful service

Over the last 2 years, after countless appeals, calls and conversations with numerous staff to cell C to comply with and honour their purchase agreement, cell C has still not taken any effective steps in the two years to respect the purchase agreement despite many complaints. On 26 January 2017, in a mail from Exclusive & Business to Business Consultant, admitted that the amount deducted from my bank account is in total contradiction to the agreement and a credit of R 3 000.00 would be passed to my account, which I cannot confirm ever happened, over a year later. At the end of April 2018, cell C still deducted the incorrect amount of R 1541.55 from my bank account; thus cell C intentionally has de*****ed me to the accumulated amount of ±R 6 200.00 (R 3 000 till end of Dec’16 + ±R 3 200.00 from Jan’17 to date) over the contract period to date. This leaves me no option but to cancel the contract given the end date is 9th July’18, as notified by cell C representative. At least, better than Cell C, I have honoured the agreement for its full duration. When trying to cancel the contract to my surprise, I was told by a cell C representative that I can only cancel the contract exactly one month before contract end date, thus on 9th June’18 is the soonest I can apply. This is ridiculous; unfortunately, the cell C representative could not provide the exact hour and minute! How, in this day and age, does cell C think that this pathetic customer service is acceptable? Frustrating and still waiting for some action and proper feedback not to mention refunds! What more must I do?