Custody In Tennessee after she has been with mother all her life.?

My children and me moved here (Tennessee) in Jan 1997 from Oklahoma my daughter was 3 yrs old and now shes 15 her father (we were never married) filed for custody and got it i don't know how i have not received any paperwork i found out tru child support that he had received custody of her because they are trying to get support from me to him after hes been paying for 3 years 100 dollars pr month i don't know what to do someone help me I don't want to loose her she has 6 siblings that they all need each other and have good family life .also i have no money for a lawyer.