CSA are essentially stealing maintenance payments

After a big admin error in 2013/2014 I was told that I owed CSA 23,000 despite only receiving payments that I was scheduled to receive and that had been taken from my ex husband.  I am parent with care with 4 kids.  Anyway, after a year of upset and hardship, 3 appeals and an independent enquiry I was given £150.00 in compensation from CSA and the slate was wiped clean.  They had broken their own rules /policy and it was proven that it was their admin error.

Now they have done it again!!  They are taking 530 a month direct from my ex husband’s salary and refusing to pay it to me.  They say I owe them money but Ive received no explanation, no letter and I have only received 530 a month since the new schedule started.  It cannot be possible that I owe them money.  They are effectively stealing the money now as they are taking money directly from my ex husband and have not paid me a penny since the beginning of December last year.  How can this be legal ????