OVERCHARGING and NO REFUNDS!!!!!

I was offered a new contract in July for my wifi device which I took up with strict instructions that it should only commence once my current contract ends which is in October. I received my new contract that clearly states that the start date is in October. End of August I was billed R910 instead of R223. I phoned to query it and they logged my complaint. Heard nothing from them so I had to continuously phone them back only to be told each and every time that the case is still ongoing and that someone will get back to me withing 24-28 hours ... this never happened! I then received my new account for R654 instead of R223 so I phoned them back and got the SAME STORY that it's being looked into and they will get back to me in 24-48 hours. I received 1 phone call back from them to say that they were incorrect and they would refund me .... still no refund! Then when I called back AGAIN I was told that in order for the refund to be processed I had to send them proof that I actually paid!!!!!!!!!!!! Seriously, the system shows that I have paid so why should I have to prove THEIR mistake!?!?!?!? I emailed them my statement .... and waited. NOTHING! Phoned back only to be told that my case had been sent to the wrong department and that they never received my email ... so now I had to resend it and ..... yes you guessed it WAIT 24-48 HOURS FOR SOMEONE TO GET BACK TO ME!!!! My first phonecall to log the incorrect billing was on 9 August ... it's now 7 October .... 24-48 hours!?!?! I think not! And guess what .... I've just received my new account for yet another incorrect amount of R654. So Cell C already owe me R1166 from the 2 previous months and the STILL can't get my account correct, 2 MONTHS LATER!!!!!!! I am beyond furious!!!! And what gets to me the most is that if you ask to speak to management you get told that they will get their team leader to phone me back .... having to deal with a call centre agent who can't help you more than telling you that your case is being handled and that someone will get back to you in 24-48 hours (the standard response to ALL queries) is totally and absolutely unacceptable!!!!!! Now let me sit back and see if this route of complaining is going to give me any joy!!!!