How can I terminate a free tier account?

I have had a free tier account for a long period now, and wanted to upgrade to paid account, as I'd like to move more worksloads to OCI.

It appears not to be possible to upgrade, since my account appears to be a "corporate" account - and not an "individual" - no idea how that happened.

I then followed another path and have tried to terminate the account - in order to make a new one. That is not possible either, as some "hidden" part in a compartment can't be deleted (by me!?). All compute instances and VCN have been terminated.