iphone 7 plus receiver volume too low

Apple store is pretty far from me and the genius bar is always packed. I finally decided to dedicate today to solve this issue by browsing through multiple forums, posts, and instructions.

1. My volume is too low during a phone call even when the volume is at maximum.

2. Followed the troubleshooting manual and tested the voice memo. Same, low volume.

3. Updated to the latest iOS11. Same, low volume. Even got the beta version of 11.3, same issue.

4. Finally had a chat with the customer service and tried doing the factory reset via iTunes, which doesn't work very nice on a pc. Still the same issue, the phone is only a year old!

5. Called back to request repair they told me it's $350 to repair this phone. ***.

I can't justify paying that much for this repair. But I'm so frustrated by having to use the speakerphone everytime someone calls me. Do you have a similar issue that got resolved?