Help my phone alarm is going off and I cant get it stopped!

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Please Help. My cell has randomly started going off saying it has been reported lost or stolen while I had it right in my hand!  I was txting and then I re-opened a web page screen ... BAM! Siren starts and I entered the wrong pin ( I was flustered and put in my Lastpass pin)  So I have logged on to Avast account and found my device but it says anti theft isn't enabled? I tried to enable and change the settings/change pin on the next screen but then it says it can't connect to my device? what can I do? My phone is an XT1575.   

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Update: resolved My phone finally showed pin screen again after 40 min and I entered the new pin voila...peace and quiet.  Uninstalling all from my phone til I get this sorted.  May re-install and upgrade to paid version.  This event was random. I still don't know why it happened and why my Avast online account showed my phone anti-theft wasn't enabled. 

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Sorry to hear about your experience.

It's horrendous when it happens.

This App is making my life a living hell.

Like you, at random occasions my phone blares out repeatedly and endlessly loudly "this phone has been lost or stolen!"

No matter what I do (frantically trying to enter the PIN number repeatedly to disable the warning), it blares this out for about half an hour!

It's extremely embarrassing if I'm with other people. Imagine what it would be like if you were in a meeting or cafeteria or public transport and your phone starts screaming out "this phone has been lost or stolen!" repeatedly and won't stop!

I am a highly experienced IT operator of over 40 years, but I can find no way to stop this. I've spent hours and hours trying different techniques.

For example, I can't uninstall the app as it's nowhere in my list of apps and also there is no apparent file for it anywhere in my phone directory.

I have got a Samsung Galaxy S6+.

How can I stop this please?

Thank you.