Can the CAB help with CSA payments?

Ive been paid £.100 a month to my ex. Now, after she made me lose money of a holiday I bought for my son and myself and not allowing me to see him, she’s gone to CSA who are saying I owe her £ 1.400 and taken £.608 already from my accounts (despite agreeing £.235 a month) and left me with little to survive for me and my new partner!!!

Im going to CAB but can they really help me? Can they get me free legal aid???

Also if anyone knows, if I leave the country, can they bother me either in Italy or Brazil (where my new partner is from?).

Thanks for any advice.
Luca