Incorrect Charge

Hi, i took out a contract in October for a Iphone 6plus, the very next day i returned the phone and took a Iphone 6 instead, on the 14th of October i received an sms that the charges will be reversed with a case #***3. I didnt worry about it and then on 25 Dec 2015, they debited my account with +/-R9000 for penalty fee, they informed me that it will take 21 days for the funds to reverse back into my account and that i should ask my bank to reverse it instead, i did that and they assured me that they will reverse it off my invoice. I again received my new invoice, but no reversal has been done. I called in again but no one had any feedback for me. I also requested they send me the banking details so that i can pay the balance of my cellphone usage, still waiting for that. I received an sms on 14 Jan 2016 to say that my line will be cut, i phoned in, but no one could help me, i demanded speaking to a manager, but the manager was busy, but i was promised i will be called back, nothing yet. i received a new case #***7. Today my line got cut, i called in but no one could help me. Im so helpless i dont know what to do, please help urgently! Samantha - alternative no ***