No sound whatsoever on phone (on calls, or while playing a video or mp3) I have a DOOGEE DG500 running Android 4.2.2. Apart from automatic updates for installed applications, no other applications have been changed recently. 

I switched my phone to the silent audio profile so that I could sleep. The next day I set the audio profile to general again, but no sound can be heard from the phone.

The phone has not been dropped or misused in any way.

I have tried turning the phone off, removing the battery for a few seconds and re-assembling everything together again but I had no luck.

How can I fix the sound?
it turns out some cold connection was the problem - not the speaker itself.
I had to open the mobile phone case and spend sometime figuring out which connection was cold. 

Once I found it I re-soldered it. If you're not into electronic your best bet is a local repair store.