Ring tone volume problem

I'm a little hard of hearing & I often don't hear my iPhone 4s ring for both phone calls & text messages. I have used the side buttons to max up the volume & also attempted to do so via the 'settings' screen option. Other people can hear it ring so it's working but not me. This was my son's phone since new & he never had any problems with this.

I could wind up the ring tone volume on my old phone to an easily heard (for me) level.

Any suggestions?

Thanks

Dave Y