Hello, We understand how frustrating it can be to not be able to hear the other person on a call. This article contains several troubleshooting steps you can try to get the sound working again. https://www.samsung.com/in/support/mobile-devices/cant-hear-calls-on-samsung-mobile
Once you complete all the steps, including the factory reset, if you are still unable to hear the other caller, 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/location or by reaching out to customer support at 1-800-726-7864.
For service outside of the U.S., please use this link: https://www.samsung.com/us/common/visitlocationsite.html