Depending on the country, yes.
By filing for child support.
no, go to child support enforcement.
Filing a joint tax return should not increase or decrease a child support obligation.
yup
Make a request from child support enforcement for a new filing, but it will not be retroactive.
No. Child support is usually non-dischargeable.
no
Contact your State's child support agency about filing a lien.
No. Child support is not dischargeable in either federal or state bankruptcy.
Yes, that is still your child and you have a responsiblity to meet the needs of that child.
Yes. Your State's child support agency should be able to help you with this.
no