notarized agreement in which ex-wife pays support rearages, i'm paying, she's not

What is the name of your state? california
my first ex-wife and i had an ageement, signed by both of us and notarized in which, i allow her new husband to adopt our 2 children, in return, i was to keep visitation, the children were to keep my last name, i'm release from paying any more child support and the ex-wife is to assume all back child support payments and rearages and any other financial child support obligations. as soon as the adoption papers were signed the ex-wife would not allow me to see my children at all, she had their last names change to her new husband's last name and i've had to pay approximately $9,000 from 1995 to present on back child support for the amount of just under $5,000, which child support services in riverside county say i still owe $2,900, which i will have to keep paying.
my question: what can i do in a legal way to recover the money that i've paid and continue to pay in which the ex-wife agreed to assume all support obligations, past, present and future, as well as the lost of seeing my children grow up and share in their lives?

[VeronicaGia]

Was the notarized agreement incorporated into the adoption papers? If not, you're out of luck.