Can the wife ask the husband to pay her alimony and her daughter's after Kuhla?

I did khula to escape an abusive husband. However, He owes me 4 months back alimony for me and my child, before the khula agreement.

This is subject to an enforcement case. He refuses to pay saying that khula means I gave up all my rights, which means also the dues from the past.

Is that correct?