Very very bas cusromer service

I orderd dishes online with smartware which included 4Kim glasses,bt I only received 3kim glasses.I called them to report that my order was not fully packed,their respond was that they have made a mistake on the adverti*****t brochure,it was supposed to be 3Kim glasses instead of 4,I tried to tell them it was their mistake not mine,and they refused to send me my remaining glass.Please help me get what is rightfully mine.