Charged for a phone I sent back

In June 2014 I received a upgrade. With the phone, I got a Samsung Gear Fit, which was not what the salesman promised me. I returned the phone and gear and decided not to upgrade just yet. When my contract actually finished (in August), I saw that I was being charged for the new phone (which I didn't have). After countless phone calls and wasting my time and money, I was eventually refunded in December, a lower amount than I should've been. I had a personal tragedy in December, so didn't have the energy to fight anymore with Cell C. Now, once again I'm being charged for a phone I don't have. My January debit order has come off and it's again the wrong amount. Is there anybody at Cell C that actually knows what they're doing? I've been charged just over R800, when it should be R250. Do they not understand that this can affect your credit record if I didn't have enough money in my account? The bank will penalise me, not Cell C, for something that's not my fault. I want my money back!!! AGAIN!!!!!!