Arthur-
I have worked in the court system as a Guardian Ad Litem and also done much mediation work with families, here is my suggestion:
First, you are working off the comments of a child. Children can mis hear things and also misinterpret things. I would first ask that you get clarification as to what is REALLY taking place, the facts...I know you mentioned that you cannot speak to your ex in person, so I would suggest a certified letter to her (make copies of everything for yourself) ask her to clear up the matter. Don't be accusatory, just state that you would like to know the facts of the matter: is she moving? Where? When? if so, what are her intentions for school/ visitiation drop offs and pickups, etc. Again, don't be accusatory, simply ask her to make everything clear. I would ask on the letter that she please reply to you within 15 business days.
Second, DON'T BE ACCUSATORY!!! I know I have mentioned this a lot, but you really don't want to put someone on the defense when you really don't KNOW what the truth is. (yes, you have heard it from a third party, but you need the FACTS from the source) Just be very plain and simple and ask for clarification.
Second (again)- if you do not get a response within 15 business days, then I would suggest a mediator before a lawyer. Judges sincerely appreciate the use of mediators (it clears some room on their dockets) and it also shows that the participants that use mediators really are looking for an amicable solution in the best interest of the child while still maing everyone happy.
Third, if you get a reply and she is in fact moving and it will impact the school your child attends, or she does plan to ammend the custody agreement by moving or changing pick up and drop off locations etc, then I would suggest getting a mediator involved if you want to save the cost of a lawyer. A mediator will help everyone come to an agreement and also make sure everything is legal and put into writing.
Forth, I cannot stress enough how important it is to get everything in writing. No matter how small of a detail you might think something is at the time, it may have huge impacts on the future. I am glad to hear that you have many documents saved. I certainly find those items useful.
Also, you are correct, If you don't say anything about this move (if it is in fact true), then yes, it is seen by the courts as a mutual compliance to the custody agreement. Since you wanted to move years ago and she said no to you moving, she in fact strengthened the custody agreement by enforcing
her rights in that original agreement.
There is a lot more information to gather before you make any drastic phone calls or decisions about what to do. After you get the facts, then you can weigh your options and take action.
I wish you luck, I applaud any parent (regardless of gender) that is willing to step up and provide for their child.