Apparently, you're confused on the difference between child support and alimony.
Child support is not deductible by the person who pays it. Child support is not reportable by the person who receives it.
Alimony *is* deductible by the person who pays it and they don't pay taxes on it. Likewise, that means alimony is reportable and taxable to the person who receives it. So if you did not report your alimony received on your tax return, that makes you in error here. You have to report all alimony received and you will pay taxes on that money.
In some states, the fact that you are married to someone else (not the person paying the alimony) is irrelevant. However, in all cases I'm aware of, when the recipient of alimony remarries, the alimony stops.
