How can the CSA take money out of the wages from my current firm?

i was working for a company that went into liquidation. the csa made an order for all moneys over 220pounds to be deducted to csa as a debt they say i owe.

My kids never wanted for anything its just i never actually paid the ex wife cash i bought for my kids direct out my pocket. i paid 4500 pound in deductions out my wages prior to liquidation but the firm never paid the csa this money .

Now the csa are saying that it is still my debt and are now deducting money direct out my wages from the new firm i am working for. How can this be right when they made the order to take money out of my previous firm wages