Sorry but no.
Only you can remove a account and to do that you need to deactivate cross save which needs you to authenticate all linked accounts.
As the authentication system is there for security reasons Bungie will not bypass it for any reason.
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But i Write with steam and they told me that my Account on steam is deleted, i cant authenticate my steam Account
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As I said only you can remove a account. Bungie will not remove the account for you for ANY reason as it compromises their security measures. Bungie has to be 110% sure before letting you mess with a account settings and will not step in as for all they know you are using a hacked or sold account. Bungie has no access to your account details which is why the authentication system is used.