Account link error

I originally have a paid account (hereinafter referred to as "A"), but I received an invitation from an outsider with a different email address (hereinafter referred to as "B") to share files.
Once I accepted "B's" invitation and was able to view the files in the BOX, I tried to link the email address from "A's" account settings, but it was displayed as an address already linked to the BOX and could not be linked. However, it was displayed as an address already associated with the BOX and could not be linked.
Therefore, I deleted the registration of "B" and tried to link it to "A" again, but the message "Cannot add because it is already linked to a BOX account" is still displayed.
The deleted account is still shown as existing, so I tried to log in again, and the account seems to exist, but a password error is shown, and I cannot even get into the "B" account because I did not receive an email to change the password.
I would like to link the "B" account to the "A" account, but the error is occurring as described above, and I am not sure how to proceed.