Charged for a new Apple Watch because I didn't send back the old one?

My Apple Watch stopped working, and I called for support. I spoke to someone named Nick, in GA. He was very knowledgable. He determined that my watch was no longer working, and sent me a new watch. The new watch would not pair with my iPhone, and he said to send it back. I did, and have a receipt to show that I did. He said that he would send me another watch, and when I received it , I should send back the watch that was not working. I have not yet received the replacement watch, but I got a notice, from Apple saying I was going to be charged for the new watch, because I did not send back the original watch. PLEASE HELP!

[Re-Titled by Moderator]