For a number of weeks I have had a problem which has meant that some calls / messages are not received / notified in time. The DND / Silent Setting keeps getting activated, several times a day. I have changed the Sound Settings to every option, many times, but with no effect.The regular option works for a while but then without warning it is switched to DND / Silent. I have now got the habit of pressing the audio button many times a day, which works up to a point but sometimes is missed. How do I get rid of the unwanted behaviour?