I just had a personal experience with Click and buy.
I had setup a Click and Buy account when I started playing FFXIV. I've not played that game now for months so I finally cancelled my service with SE. I then tried to login to my click and buy account in order to block payments from that side.
On their account login, I provided my user ID and my password and was then surprised when it asked for my date of birth. I've never seen any login use a date of birth as effectively a second layer password. In general, I never provide my real date of birth to any service on the internet as it is not relevant to any commercial transaction.
Through email and phone support (over an hour on hold before getting a person), they informed me that in order to access my account, they needed me to photocopy either my passport or my driver's license, attach it to an email and send it to them as Proof of my birthdate for them to reset my account. I had sent them emails from the email account on record. I gave the agent the correct answer to my regular security question. I was even willing to verify the credit card number on the account over the phone. Nothing doing. Send copies of critical ID or GTFO.
I'm definitely not sending copies of critical identification to another country using unsecured email over the internet. On the phone, the agent also said that this same process was necessary if I needed to get any money back from Click and Buy (such as for an unauthorized charge being made to my account).
I've cancelled my click and buy account rather than send the info.
I'm going to think about this for a couple of weeks. The agent did confirm that I could, if I wished, create another account after my current one is cancelled. I could even still give them a bogus birthdate - I just need to record what I entered so I can use it as a password in their screwy system. I'm not sure it's worth it.
I'm betting that cancelling my existing account with C&B could be terminal wrt my SE account. I'm betting it's not possible now to link that to different, new C&B account now.
edit: Just noticed the post above me. Maybe I can link it to a different C&B account. I'm not sure I want to bother though.