How can the CSA just do this?

Hello, I have had no correspondence off the csa for nearly 4 years when suddenly last Saturday the 22nd I got a phone call from my ex wife saying the csa had set up a deduction of earnings of £503/month.

I thought the case was dead as my kids are 28,24and17. Surely the agency has to notify me regarding this and surely they cannot just slap a bill like that in front of you?

The first payment comes out in December and will leave me with £700 to live on, with rent and bills I just cannot survive. Why did the csa not contact me to tell me to come up with a payment plan?

Feeling totally dejected and suicidal as just can’t operate now.the csa refuse to budge on this despite my calls all week, can someone please help me?