Yet another upgrade headache

I should have learnt from my shoddy service when I upgraded two years ago but sadly not. In November 2015 I called the call centre and ordered an iPhone 6S on upgrade. Zaheer Hendricks processed my request. In December I followed up on delivery of my handset and ETA was still unknown. As I was traveling overseas the only option they gave was for me to cancel the order, which I did. I received confirmation via SMS on 12 December. On 6 January the handset was delivered to me so I refused delivery and sent it back with the courier. I have followed up twice with their call centre regarding the cancellation and I am still being charged for the handset. Their call centre keeps cutting me off now. I am at my wit's end with their appalling service and system. I will be cancelling my contract.