For those of us that use Skype you will sometimes get calls or people wanting to call you that you do not know.
You can stop this by adjusting your settings in Skype.
You open Skype
Go to options
Then to privacy
You are now after “Allow Calls From”
Change this to Contacts
Next you are after ” Receive Calls To My Skype Number From”
Change this also to ” Contacts”
More information can be found at the following CNET article