Divorce Support Forums: Multiple trips for Child Support Modification

I am divorced 10 years with two teenage daughters. One will grduate in 2007, the second in 2009. My ex has taken me back to court for modification of child support at least 5 times in 10 years. Each time the court has made no modification to the child support. Now my ex has a motion before the court that I pay less child support than my income would require, and have done so since 2003 so she wants to have the difference in what I did pay, which was set by the court, and what the guidelines say I should have paid. In our last court proceedings 11/2003, the court made no modification to child support, and I was told from that date, 11/2003, prior, for the first 7 years of child support, the ex can not sue me for the difference between what was paid and what should have been paid by the guidelines. Does anyone know if that is correct? Once a court makes a ruling on a motion, the same motion can not be ruled on again, unless there are unusal circumstnaces. If you know, please advise.

Part Two. In the same scenario above, I paid directly to
my daughters in the form of college tuition program, health related issues, school supplies and lab fees, personal care items for use at the ex's home, clothes, travel, cash, etc what would equate to more than double the amount of the difference of child support paid and what the guidelines state would be required. Example, the guidelines say I should pay $300 more a month but I was spending a minimum of $700 extra direct to my daughters. Do I get any favor with the court for this additional spending directly to my daughters? Can I use this additional spending to offset any judgement against me? Please advise if you know.
Thanks for any help.