Troubleshooting
Official telegram.org Source
To delete a contact, open a chat with the person, tap the title in the top area of the chat screen to open their profile, then tap on (⋮) in the top right corner > 'Delete contact'.
If you want to delete the contact completely, make sure you also delete them from your phone contacts. Telegram stays in sync and will add the contact back if you don't.
Official Telegram Reference: https://telegram.org/faq
Part of the TGWAY.com Official Telegram Knowledge Base (98 Verified Q&As).