Save your phone records showing your failed attempts at contact. She is likely to try to claim that you never tried to see or talk to the kids. Keep a journal of everything that happens regarding her failure to follow the court's orders. The kids should have spent the summer with you, so it is proper that you should cite her with a violation for not making that happen. Don't wait too long and make the same mistake you made after her move-away.
She has no legal right to do this, but if you sit on your thumbs she can get away with anything. Get a lawyer. If you can't afford one, file anyway. Try to file locally, but your local court may reject your petition because you waited more than 6 months after she moved, which changes jurisdiction to her advantage. I sure wish you had found us in the first few months after she moved, but you still have the legal rights to contact with the kids and she has no chance.
There is going to be money involved, especially if the jurisdiction is in her state, as it probably will be. Your H will have to travel because it is potentially devastating to his case if he fails to appear in court. I'm not sure why there has been virtually no attempt to travel to the state where his children live so far, but he is probably going to have to start doing so until he gets this resolved.
Part of your petition should involve mandated phone contact. Don't let her get away with this.