Exhange

Nov last year someone bought me a Fitbit 3 which was in special for R1900 and unfortunately I’m no longer I contact with a person but Fitbit is still under warranty and I’m told I can change it as he need to change it. How do I get hold of him to change the watch we lost contact I’m not sure where he is. I’m told I can’t change how is that possible I don’t need refund I need exchange. The guy communicating is not even willing to go a mile to assist he just telling me about the procedure.