wrong steam account accidentally linked to EA account

Hello everyone, 
My daughter accidentally linked her Steam account to my EA account. Unable to restore the link betweeen my personnal steam account and my EA account because of a 6-month delay thing.Consequences are that I cannot play with my SIMS 4 DLC's from steam store and from EA store at the same time.

I can prove that I have access to the linked Steam account and the one I want to restore. But the support.

The technicians in the support chat can't help me and don't want to escalate my case.
Is there a way to solve that?

Thanks!