iplay40 speakers don’t work

Speakers of iplay40h always have no sound suddenly while using. I’m too confused.

Anyone face this problem?

Do you have sound through a bluetooth device – headphones, speakers, etc?

No, I checked all related devices.
It works normally for a while, then suddenly muted phone speaker, can’t play any sound files or making audio call. No sound at all.
I notice sometimes after making OTT calls, it muted phone speaker immediately then.
Too confused. A little bit disappointed with Alldocube. I hope everyone faces the same problem with me can point out some way of resolving asap.