Stop receiving unwanted chats and calls
If you are getting chat messages or calls from people you don’t know you may need to change your Skype privacy setting.
You can change your privacy settings in Skype to only allow calls or chats from people in your Contacts list who you have authorized.
Go to: Skype -> Preferences -> Privacy. Check the box next to the option “Only people whom I have authorized can start chat”.
Then random strangers and people who are not on your contact list cannot contact you anymore.