advice about ssi disability and child

hay all i need some advice on the following.
in 2000 i applied for ssi disability. i won my case in 2004. my back pay was about $24,000 and my daughter's mother (whom i never married) got around $11,000 in one lump sum and $350 per month until she is 18.
the mother told me she was going to put the money in an account for my daughter for college and so forth. i also am paying $200 a month for child support thru the courts system. i have always paid my support.
my daughter will be 18 yrs old in november and her mother has been calling demanding that i pay her $1000 for my daughter's college or never see her again.
am i right to think that the back pay sent to her should have gone to my daughter as well as the monthly amount? she claims it was child support but i was paid up and in mo. child support is only paid if it comes thru the child support family division which mine has for 17 yrs ?
i am 47 with a disability and will never work again ?
thanks for any help bill in missouri