Upgrading to 18 from 16, and need to transfer Activation key from one account to another

Hello,

I have two v16 Parallels Desktop for Mac licenses. A couple of questions:

1) Can I purchase upgrade licenses to V18?
2) One of the Activation Keys has been registered to the user personal account, but I would like to transfer that Activation Key under my account instead since I do the purchasing. Parallels Support KB suggest that only Customer Service can make the transfer, but the user account's email support option is not available. So, what other alternative method can I use to transfer the key?

Regards,
Immanuel