Is there a statue of limitations on paying child support?

Baby was born in 1966 made regular payments for years. I was suppose to pay until she was 16. I paid ten dollars a week for years. Stop paying so they took my income tax return and all money received from the goverment and they continue too.. Got a letter that says I owe 15,000.00 or they would seize all of my assets. I know I do not owe anything like that she is now 43 so what can I do. I just retired at 72 and have little money to pay anyone. I did receive a lump sum payment from my 401k that amount to little for I never put anything in there. Please I need some advice. I do not mind paying if they say I have to but this is all wrong. They gave me ten days to respond but they sent the letter out today 3/7/09. Letter is dated 2/25/09. The child was born in Washington DC and still live there. After 43 years I think what I paid and what the government took out has got to be enough