Being billed for an item returned in December 2014

I was contacted by Mondo cellular about a promotion. I accepted the offer telephonically but when I received the item I realised it was not going to work for me. I immediately contacted them and they arranged for a courier to collect the item from me on the 18.12.2014. To my ama*****t I was charged in January and again in February 2015. I contacted the call centre and spoke with Claudelle who assured me the problem would be resolved. In march and April....still being charged! I called again only to be told that Claudelle was unavailable and that Cashnee would assist. She too assured me she would investigate and get back to me. Surprise, surprise no response! In May and June I still get charged. I called again and spoke to Cashnee who was adamant that she would get the issue resolved....I got charged again in July! I then called again and spoke with Shaista this time who checked and assured me that indeed they have a record of the item being received back but she was not sure why Vodacom had not been notified. She assured me she would take this up with her manager and get back to me before the end of the day.....that was 2 days ago and guess what....no call back! Really???