Hi. I've been stressed out for quite some time because my ringtones can't be heard or are very soft. I have not been able to receive the calls, often missed them. The problem is, I did not set my ringtone volume to the lowest or to silence. Once, maybe by a mistake. But these have been kept happening a lot, surely it is not my mistake but the system's. Can somebody tell me why? How to fix this thing? 

Thank you. Hope you have a great life.