someone has already added that key as an access key to a repository.

[iam_numlock]

I cannot add my SSH key to my account because of this: "Someone has already added that key as an access key to a repository."

I have checked all the places (company user, all the repositories I see etc.) but this key is not associated to none of the repositories nor users I know of.

I have tried to SSH bitbucket.org, but is does not say any details:

$ ssh -T git@bitbucket.org
authenticated via ssh key.

You can use git to connect to Bitbucket. Shell access is disabled

[Nic Brough -Adaptavist- · Accepted solution]

There's no easy way to work this out because the keys that belong to other accounts should not be shared.

If you shared the key with someone or used it with a different account, you should already know who it is.  If someone gave you the key, you will need to ask them.  

If you have no luck chasing it down, you can raise a support request with Atlassian, and they can search out the key for you and identify the account you shared it with.

If you don't want to spend ages chasing down the share, you can (and should) create a new key for your account and use that instead.

For a better explanation, see Theodora’s answer on Problem adding SSH key: "Someone has already added that key as an access key to a repository."