Deleted email address still there, hidden

MacOS Catalina.

An email address deleted from Contacts shows up when I type the first 3 letters of the correct address in a email TO: box. (both the current correct address and the erroneous deleted one are there to choose from).

I can't find it in the Contacts list locally or on iCloud. How could mail find it if its not there?

I sent it by mistake and don't want to do it again :-( I need to delete it. Please help me find it.

Thanks