Divorce Support Forums: Support Modification

I'm a little confused on what to do and would appreciate any advice. My ex lives in Missouri w/ my girls (16 & 18) and I live in California. We were never married. Our financial situation has changed dramatically since our original agreement over 10 years ago. My ex is now working full time and earning a great deal of money, (when agreement was made she was unemployed). I just started a new job after my job of 10 years relocated to another County. I am making less $$ now. I have tried to contact Family Support in Missouri and they said that even though I pay through them, no court order has been made - they wouldn't give much more info and not a lot of help. I see my children maybe 2 weeks out of the year, (if I'm lucky), and would love to be able to spend more time with them, but my ex and her mother will not allow it - at one point my children were living full time with the grandmother and my ex was collecting the support - she did not notify me of this as she does not notify me of any changes involving the children even after repeated requests. My ex also vacationed with the kids about 2 miles from my house 3 weeks ago and wouldn't even let me spend 10 minutes with them even though they were so close. It broke my heart. How do I reduce my support to her now that my eldest has graduated high school? Please help! I don't have a lot of money for a lawyer and any advice would be appreciated...
Thank You!

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