How to get ticket transfer proof from FIFA website

I originally purchased four tickets to the Germany vs. Curacao game, then couldn't use one so I sold it on StubHub. I transferred the ticket to the provided email address and got no emails saying there was an issue. I attended the game with my kids and there was definitely someone sitting next to my son in the seat we sold.

Weeks later, I get an email from StubHub saying the sale was canceled because there was an issue with the transfer. They say they need proof that I transferred the ticket to the right email address, but in my FIFA purchase history I can only find evidence of the transfer to a NAME vs an email. StubHub won't accept this as proof. 😡

Has anyone else experienced this? Anyone know how to get proof of the email that a ticket was transferred to? I sent an email to the FIFA ticket customer support email, but that feels beyond pointless. Help!