Disgusting service

Purchased a ring from Sterns in a KZN store around 2015. Possession of a valid certificate. Last month the diamond stone fell off the ring. Took the ring to the Pavilion store in Durban. The assistant manager did a test on the stone and advised that the stone is **** and not a real one. He indicated that if a stone turns yellow or brown the stone is not authentic. He also mentioned that he needs to send the stone in for a QA report and this may take around 3/4 weeks. Earlier this week received a call from a Patsy querying why the ring was purchased if the stone was yellow or brown. How pathetic - firstly I am not a guru or fundi to notice colour of stone and furthermore why was your store selling yellow or brown stone in the first place. My ring is still with the store and no one seems to assist. As for the customer service department it is a joke. No one returns your call. Will now take business elsewhere as Sterns is now selling **** jewellery.