Hello, I understand how frustrating it is when the speaker is not working correctly. This article contains several troubleshooting steps that may help, including testing the phone in Safe Mode. https://www.samsung.com/us/support/troubleshooting/TSG01001255
Once the troubleshooting is complete, if the speaker is still not working then it is recommended to have the phone evaluated by a certified technician.
You can use the following link to find a list of service centers in the U.S. that can do the repair: http://www.samsung.com/us/support/service/ or by contacting customer support at 1-800-726-7864.
For assistance outside the U.S., please use this link: https://www.samsung.com/us/common/visitlocationsite.html