What David P2 already said. OO It's the Truecaller app.
Open your people hub, tap the ellipsis (three dots at the bottom), choose "filter" and uncheck the Truecaller app there. Problem solved.
I think there's an option in there to tell it not to save blocked contacts to the address book - that will help in the future, but for what's in there already you'll have to remove them manually). Best way is via the People link in Outlook.com/Hotmail.