No Sound When I Am Sent A WhatsApp Video

I have no idea what has happened to my phone today but all of a sudden I can no longer hear the sound when I play a video sent to me via WhatsApp. I have a brief moment of sound then it cuts out, like someone has pressed mute. If I pause the video then press play again, I have again the brief period of sound then nothing.

I also have a problem sending Audio recordings. One minute it works and allows me to send them, the next I get the following error:

application error failed to save voice message

When I press the Mic button and get the error it makes a "double ping sound" and when the error message comes up I get a very brief red line across the top of the App.

I sent a video today and when I played it back on my phone the sound is perfect, I just cannot hear on videos sent to me.

I have deleted the App twice now and even deleted the file from my iTunes before going to the App Store and starting again. The sound is switched ON in the Microphone setting. I am at a total loss at to what has happened.

Please help.