Hi @ludy ,
Do you hear the ringtone when you go into settings and change the ringtone and the phone provides a brief audio sample of what it sounds like?
Alternatively, when playing music from the phone, can you hear it coming from the loudspeaker in the phone or if on a call can you hear the other person when using the phone in “loudspeaker” (or hands free) mode?
If not then there is a problem with the phone’s loudspeaker. This speaker is the same one that is used for the ringtone and notification sounds.
If you can hear music or voice from the loudspeaker, try starting the phone in [http://howtosafemode.com/2709/how-to-turn-on-safe-mode-on-blu-vivo-5|safe mode] and check if the ringtone/text notification tone etc work OK.
If it does then a ''downloaded'' app is the cause of the problem. The trick is to find out which one is the culprit. You’ll need to uninstall each downloaded app, one by one, and test the phone in normal mode, between each uninstall to check if it works OK. When it does the last downloaded app that was uninstalled was the cause of the problem.