Disgusting customer service

I am completely shocked by the response of the sales assistants at Sterns at Kenilworth Centre. I bought a ring with my Jet card in October, a month later I noticed that the ring was missing a few stones. I have been to the store for the fourth time now and still they are telling me that I cannot return the ring without the invoice or without permission from Head Office to reprint the invoice from their system. I am completely disgusted by their non-chalant attitude and no remorse or empathy shown for me purchasing one of their rings of very poor quality. They should be ashamed. I would feel embarrassed if I sold something to someone that showed such poor quality. I am not leaving it and will definately take it further.