Another excellent chat with support. The two accounts, old and new are a bit confusing
The chat person patiently analysed the problem in detail. There is something strange about my two accounts in their records, he said.
He suggested I reply to the CDOC Case Management email asking whether the game license can be transferred to a different account, since the original account could not be recovered.
I have done that and have a transcript of the chat, all 80 minutes!