I just got accepted for Supplemental security income here in Washington State and I went to the appointment and they said I was going to get a back pay check at some point. I owe a lot of back child support (I was 15, the mother was 14 and when I didn't want to be her boyfriend she filed for child support and got money while my grandmother took care of the kid, then kicked me out because the mom said if I lived there she wouldn't get the money anymore and wouldn't let my G-ma have our kid... So I was homeless and jobless for around 10 years) ANYWAY I owe a lot.

I was wondering:
A) can they take the whole back pay check?

B) If they can how will I know it's happening? Will they send me a letter first or will the money just never arrive.

This money is really important because I owe on rent for at least 2 months on top of vet bills, (I think my dog is sick again too)and other random bills.

I do want to get the child support out of the way but even if I pay it the mom will get the same amount and either way it's not going to the kid.