Hi,
OK....understand the problem better.
I'm not sure a new account was needed. You can do a Support Case to change the old Auctiva account name and disconnect from old Buyer ID by cancel Token / reconnect the account to the Selling eBay ID. I believe that's similar to changing the eBay ID (new name) procedure. That way you could keep any customizations, profiles, saved listings, images, etc.
I would file a Support Case and explain exactly what you want to do. I do think you have to stop listing temporarily to get the transfer done. Hopefully, they can give you step-by-step instructions and help with the back-end changes for the ID.
Danno