the burden of proof is willful non compliance of a court order. Send letters to the ex demanding that there be compliance with the order. then if it happens again file for contempt then use the letters to show the court that you tried to resolve it short of a hearing. If you continue to get massively jerked around then you can go for custody. Contact my office for free consultation.
I am not sure what you are "supposed to get" because your facts are kind of unusual and not what we usually see in time sharing plan. Proving that you're not getting the time sharing is difficult, but it can be done. You really ought to hire a professional to deal with this and I'd be glad to talk to you about it. If you go it alone I do not think you will succeed. Call my office anytime for a free consultation.