In order to determine what the issue is with your device, please perform a hardware test on your phone. To do this dial *#0*# into your telephone keypad > tap on 'Speaker' > listen to the sound quality. If there is no sound or if the sound quality is poor, there may be a hardware issue with your device. If this is the case the best thing to do is to take your phone to one of our Samsung Support Centres: https://www.samsung.com/uk/support/
That indicates that there is an issue with the phone itself so please contact our Support Team to arrange a repair for you using the link provided above.