I have an agency upwork account and a Freelancer upwork account too.
Can i hire (as an agency) my own Freelancer (atatched to this same company)? Is it something that I can do or not?
No, you must not hire yourself, as that is considered feedback fraud. Having two or more accounts, which you also seem to have, is also not allowed.
Furthermore: agencies do not hire freelancers.
You can create an agency using your current freelancer account. There is an option under your Settings. You as a freelancer will then be the owner of the agency and can work with the team of other freelancers. Agencies on Upwork work on contracts but don't hire for contracts.
What I believe you are referring to is a client account. You can use Upwork as a client to hire other freelancers and agencies to complete your projects but you can't hire yourself. That would be a serious violation of Upwork ToS.