I’ve paid CSA and now it’s due to stop they demand an extra £13,000!

Rang csa in January 2015 as payment on attachment of earnings should of stopped november 2014 as child turned 20 that month,The c,s,a advised me I owed they 13000 pounds from 20 years ago,How can that happen,was not earning that type of money then only earning 150 per week on average,why did they want 13000 pounds,not only that now found out the child came out of education in 2011,the payment should of stopped then,but the c,s,a carry on taking till now and forever,now question c,s,a on how this monies outstanding,they wont give any answer but told me I owe this money when I don’t.

Also In 2005 they said they owed me monies but now that not correct,because I have ask for this to be looked at sending letters to M.P ,THE C.S.A. AND THE GOVERMENT STILL NO JOY,Now have an order against me for something not owing and just advised on this by call from C.S.A, The problem also had an attachment of earnings for 19 years which was set by c.s.a and nobody can change that ,why this bill from 20 years ago and why didnt the c,s,a stop payments in 2011 when they were not entitled to more monies,need help what can I do, 20 years ago if only earning a average 150 pounds how can they take equivalent to 103 pounds per week into account also why wont they listen about when payment should of stopped in 2011.why do they just want to make figures up and make peoples life hell,not just that but make myself ill with stress and depression and nearly taking my life on couple of occasions.