charged after the account has been settled

I am so disappointed with cell c and I don't think I will refer anyone. I always heard stories about cell c but I didn't want to judge them until I took a contract phone with them about 5 months ago. Come march, I decided to settle the amount & went to cell c in festival mall to ask for a settlement amount and when I got there it was like I'm talking another language. I then decided to contact the call centre & I don't remember the consultant's name but I am sure your phones are recorded. I asked for a settlement amount and the consultant said its R7832.50 and I paid via eft on the 1st April 2015. I then asked what do I do after making a payment and he told me that I can fax the slip or phone to confirm if indeed the payment went through. I faxed the proof and also phoned the call centre the day after the following day and was told that its cancelled. To my surprise I was debited today with R646.71 that I know nothing about until I spoke to Amelia Zulu (cancellation dept.)who refused to call the manager on the line for me to speak to her. As a customer I have the right to speak to the manager unless if I am wrong. April 20th I wasn't debited but now I am debited.