Billed for free upgrade phone - can't get refund

After numerous calls from MTN (whereby I declined an upgrade every time) I opted for an upgrade to the (then) new Samsung S5 phone.<br> <br> MTN ***<br> <br> I received the phone on the 29/09/2014 and signed acceptance.<br> <br> A month later the amount of R4699 appeared on my invoice and the amount was automatically deducted from my bank account. This was a normal upgrade whereby you sign a 24 month contract which includes the phone.<br> <br> I have been trying now for months to get this money back, with numerous visits to the Tygervalley branch, escalation after escalation, but no results - or even feed back.<br> <br> The people at the branch reckon the transaction is \locked"and they do not have the authority to open it.<br> <br> I'm sitting with reference numbers coming out of my ears"