BTT - I don’t use outlook but was happy to see this thread - just yesterday I was trying to help someone who had some computer challenges with Windows 10. Was able to help her with everything except your same issue. She was given a laptop and can’t delete the old contacts. I’ll read through this later and hopefully can give her an answer.
I even went so far as to delete the ‘People’ app, since Windows Help told me it was really my ‘contact’ list.
Didn’t help! the contacts still showed up even after deletion!.....................