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 have the phone examined by one of our engineers. You can arrange this by contacting our Support Team.