International call charges but never used cellular service!

Today I received this text “AT&T Free Msg: Courtesy Notification. Your international long distance call charges exceed $200. Visit att.com/global for rates and details.”. My boyfriend just moved to China and we have been using FaceTime audio to talk. I know it is FaceTime audio for sure because in the information it says how much MB of data was used. A normal mobile phone call does not state data. How am I being charged for international calls when FaceTime uses WiFi/data unrelated to cell service??