It isn't possible, to do the unlink part yourself.

only support can do that.

here you can get all the info,
https://help.ea.com/en-us/help/account/linking-your-origin-account-with-your-psn-id-and-gamertag/#un...

here you can get all the info, about delete account.

https://help.ea.com/en/help/account/how-to-close-your-origin-account/

Delete account

• Account deletion is permanent and can never be reversed.
• Deleting an account erases your personal account information from our account and customer services databases. Permanently.
• Once your account is deleted you’ll lose access to your games, subscriptions, and in-game purchases associated with the account.
• As a condition of account deletion, we also require that you stop any further use of our products and services.
• You will no longer get transactional or marketing emails you opted in to.
• We can'trestore your deleted account or transfer any information, data, or games to a new account.
• Even when we delete accounts, we will retain any data we need to comply with legal obligations (like paying taxes and enforcing our terms), to ensure the security and integrity of our systems as well as ensure the rights and freedoms of others (including EA).

if you need more help for your account. Contact support,
https://help.ea.com/en/

or if you are on Twitter.
https://twitter.com/EAHelp.

or if you are on Facebook.
https://www.facebook.com/EAHelpHub