Why is unlinking my PSN account so much hassle?

This is a new account which I was forced to make recently after finding out that my old account, Tryst, which participated in the 1.0 Open Beta, 2.0 Closed and Open Betas and the PS3 Beta, is unable to play Final Fantasy XIV on PlayStation any more because the PSN account it is linked with is blocked.

My old PSN account is blocked because back in May last year I was double-charged by Sony when buying the game Beyond Two Souls. I purchased the game, but through some mishap they managed to charge me twice for it. After sitting on the phone with Sony's support for around 3 hours back then they finally told me they couldn't refund me - so I did the logical thing and went to my bank and got the double-charged payment reversed.

Alas, Sony banned me for it. Great.

I recently upgraded from PS3 to PS4 after not playing Final Fantasy XIV in a long time (since late 2013), after receiving an email about their upgrade campaign. This got me interested in the game once more, so I upgraded. After waiting a few hours for it to finish downloading and patching, I tried logging in on my old account only to be greeted with a message saying that I can only access my FFXIV account on the PSN account it's linked to. Impossible.

I contacted Square Enix's Support Team and they told me the only way for them to unlink my old PSN account would be for me to provide details of communication with Sony. As my communication with them was entirely phone-based, this isn't possible.

Why is it so much hassle for me to get my old PSN account unlinked from my old account?