How to unlock device?

A while ago, I removed my SIM card from my Samsung tablet. Ofcourse this triggered the siren. Since I couldn’t remember the PIN code anymore (any PIN code that I may have used doesn’t seem to work), I went to my Avast account online and mark my tablet as found. Everytime I restarted my tablet, the siren went off and I had to unlock my tablet by going to my Avast account online. I got fed up with that, so I removed the device from my Avast account, hoping that it wouldn’t trigger the siren anymore. Unfortunately, I just turned on my tablet and the siren is going off, even though I removed the device from my Avast account. I can’t take out the battery (you can’t open this tablet), so I can’t stop the siren and I can’t use my tablet anymore. I can’t put any new SIM card in my tablet either, so I can’t send an SMS to my friend to unlock it. Can someone please help me to unlock my device?

https://www.avast.com/faq.php?article=AVKB135
https://www.avast.com/faq.php?article=AVKB127

Removing the device from your account just means that.
Nothing more, nothing less.
The application is still on your device and keeps working (hopefully) as it should.