Samsung won't replace faulty S6!!!

We are in the unfortunate possession of an S6 which we have taken to the Samsung Centre in Century City 3 times this year already. The phone won't stay on silent (which is crucial during mtgs) & the battery depletes within a day. My boss received this phone last August and for the first couple of months it worked perfectly. I called the Call Centre on 27/05/15 to ask if we can't have the phone replaced since we have taken the phone in twice already & was told that it needed to go in three times before they will replace it. I have been to the Samsung Centre again on 24/06/15 & it is still giving problems. I called the call centre today to find out when the device will be replaced & was told to go to the centre again for a reference number & then I must come back & call them & provide the reference number!! Seriously!!?? And then they can't tell me how long it will take for a decision as to whether we get a new phone! My boss has asked me to cancel the contract and to toss this phone and we won't be dealing with Samsung ever again. We work for a large company with branches & franchises across the world & will certainly be spreading the word on this one. Very unhappy!!!