I believe my husband's ex-wife has been claiming the children as tax exemptions for years now and their divorce states that he could! What do I do?

My husband was killed in Iraq last year and he had was previously married with 2 children. Their divorce papers state that he had the right to claim the children for tax exemptions. Every year we file and are rejected and have to submit additional paperwork including the divorce papers. We have always received our refund but it is always extremely delayed. She still receives her full refund with no penalties. This year because he died in 2008 and I am his widow and was in charge of the estate has been challenging for filing but again my refund has been rejected because the SSN#'s have already been submitted by her! She also receives gov't assistance which she does not need because he had to provide health insurance per the divorce but she has them on hoosier works and now she also has Tricare since his death. She claims assistance for lunches at the children's school because she claims that she is a single mother with no support... which is a lie.. My husband and I have paid child support per the courts and have never been late. She has begged him in the past to allow her to claim the children every other year and she would split the money with him because she states she would get a larger refund. My husband was iriate and told her HELL No... he always talked about turning her in but he didn't know how or what to do? I am so tired of her lies and deception. I struggle to survive without him daily while she is living it up! HELP!