Indifferent and non-responsive service

I bought a 2 x converted lens from New World in October 2014 as I had an insurance claim and the insurer instructed me I could only buy from them. Upon learning that the lens does not work with the autofocus function of other lenses, I took it back to New World in November 2014. I phoned the saleman, Werner, at least once a month to follow up. He always promises to come back to me promptly, after speaking to the supplier, but I have not once received a return phone call from him. I also went in to the store repeatedly to speak to him. In February 2015, he informed me that he would ask the supplier to deliver a replacement directly to me. In April, I phoned him again and he asked me to speak to the supplier myself. I informed him I do not want to speak to the supplier, and that they could offer me another lens (an inferior 1.4 converter). I then spoke to his manager, Mukesh Bhima, who informed me that he would order a replacement directly from the manufacturers and revert within a few days. To date, I have still not received any feedback. I am also not happy with their condition of not refunding cash but only providing the option of exchange for a product of the same value.