Can't add my SSH key

I keep receiving the message 'Someone has already registered that SSH key.'
I have only one account one bitbucket with username sindhus.

Some years ago I had a bitbucket account with username 'sindhu' but then I have deleted the same and now someone else is using that account as far as I know.

Because of this am unable to access my bitbucket account via ssh.
Please resolve this at the earliest for me, thank you