How to rectify that receiver can not hear properly.

Hello Raj Perera,

Thanks for the question. After reviewing your post, it sounds like you are having trouble with the receiver. I would recommend that you read this article, it may be able to help the issue.

If you can't hear a person on a call or voicemail or if the sound quality is poor on iPhone - Apple Support

Thanks for using Apple Support Communities.

Have a nice day,

Mario