Hi Muhammad,
Sorry I did not see your question sooner. As Mary mentioned, the Skype plugin has not been officially updated since the version for Moodle 2.7. Just because I used to use Skype before I retired, I have generally kept a version working and available from my github account. If you go read the comments at https://moodle.org/plugins/mod_skype you will see details on how to get a copy. I am currently using it on Moodle 3.2.1+ with no apparent problems, other than one warning about the Update this Skype button being deprecated. The warning can be safely ignored.
The plugin is not a graded activity or anything. It just gives you a way of automatically listing all users in your Moodle site with a Skype ID entered in their profile.
On more than one occasion the maintainer has mentioned releasing a new version soon...but nothing yet for a good while.