Can’t Access this group or any other? Follow these steps
1. Go to the Telegram Web(https://web.telegram.org/z/) and login.
3. They will Send you a code on the Telegram App. 
4. Once you’re login,click the 3 dots on the upper left corner and go to settings.
5. Privacy and Security
6. Scroll Down and make sure this is Checked.
7. Restart Telegram App.
Done