How to delete Telegram account
From the Telegram help and support page, it is clearly stated how you can delete your telegram account.
It is recommended that you use non-mobile browsers to log in using your mobile number and delete your telegram account.
Click the following direct link which will ask your mobile number associated with your account.
Then you will receive an authorization code through your Telegram account which will help you to delete your account.
Deleting your account permanently removes all your messages, groups and contacts and can not be undone.