What makes you think your account was deleted?
If you lost your serial number (which, obviously you did) you can simply go to https://www.bandicam.com/buy/
and enter your e-mail address on the bottom of the page.
Try out multiple addresses if you don't remember which one it was exactly.
If you can't access your mail account, please contact either your mail hosting service or if that doesn't help I'm sure you will find a way to regain your serial by contacting Bandisoft.
I hope I was able to help you,
Thank you for reading my post. I hope you understand my "English".
I'm the German translator for some of Bandisoft's products and websites
(mostly Bandicut and Honeycam).