The IRS has a taxpayer help hotline and a taxpayer advocate service that may help you in these cases. Or, ask a local CPA.
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I agree that you can consult IRS or a competent tax return preparer. Whoever you consult will need more accurate information than your question includes. For example: the date of the final order of divorce [get it and copies of documents from your lawyer or the court]; a copy of the divorce decree and, if applicable, the settlement agreement; the dates during which you and your child resided with your former husband; the amounts or approximate amounts of support furnished by each of you; the date when each of you stopped residing with your former husband. Almost all answers to questions posed on AVVO depend on the accuracy of the factual circumstances presented; change the 'facts' and the answer also changes in many or most cases.