Rachel,
Just when you start living your life, they come back in and mess with you in one way or another...too bad it has to be through a 10 year old. I would just keep it simple and to the point. Contact with your 10 year old daughter is unacceptable especially without your knowledge. If you find that they have contact with your daughter again without your knowledge, especially involving picking her up and taking her to a location without your knowledge you WILL file a restraining order against them as that is kidnapping. Make a copy of the online conversation for court documentation just in case. Also, I would delete the contact info from your daughter's online account so they cant mess with her head.
So sorry to see you have to go through this crap, hope it goes away fast for you.
Lots of hugs!!!!
- Kris