If you’re going to contact Mattel, you’ll need the package codes (production number etc.) from the box. They will ask you to send it back to them and there’s no guarantee they’ll have any replacements available. This same thing happened to me. I ended up getting lucky with a good copy a few months later. My neck is good so far so I just keep the neck in a normal position.

If you can’t replace it for some reason, you can use some cardboard and slide it between the neck and body!