This is a small, but very good working, instruction how to solve this problem:
1. On the right side of the page, everyone has a side panel with contacts. We need the rightmost corner and the icon with the settings:
2. Click on it. We are interested in two items: chat and video/voice calls:
3. Let's start with video/voice calls:
Next, choose the appropriate option for you, I chose the last one:
Click "Disable". It is done
4. Next step is turn off chat
There are three options:
a) turn off chat for all contacts
b) turn off chat for everyone except the contacts you selected
c) turn off chat for only some contacts
Choose the appropriate option (I chose the first option - turn off for all contacts), click "Okay" and in my case see the following:
That's all. No video/voice calls and annoying messages from unwanted users
If the information was useful for you, you can thank with Merit
