Why am I unable to change my যন্ত্রপত্র address to one that was used দ্বারা an account I deleted?

That's right, I'm outing myself. I the ব্যবহারকারী নাম change advocate had actually created this account to replace another with a ব্যবহারকারী নাম I didn't want anymore. The difference is that I'd barely used that account, I hadn't established myself with it and had nothing to lose.

Anyway, that is beside the point.

I'm quite certain I deleted that original account when I created this one but I'm not able to convert the যন্ত্রপত্র address it used to this account as it tells me it's already registered to an account.

I'd let this go for all these years, so why do I care now?

Well, the যন্ত্রপত্র address in প্রশ্ন is the one I actively use for communities such as this so it's always been a preference but am also feeling a bit weird since I had to use it when I emailed FP yesterday to see if they take ব্যবহারকারী নাম change requests.

So I'm figuring it's time to get this figured out.

Any thoughts?