Any advice???

Ok.... Here's my story.

I graduated from college in 1991 and had about $10,000 worth of student loans.  I paid most of that back but then went bankrupt in 2001.  Went through a nasty divorce, won't go through that here.  Since March of this year, I have been receiving very aggressive phone calls from 2 collection agencies one of them being Collect Corp.  They are saying that I received more monies than I was entitled to of my grants. 

Now the thing that gets me, is that when I went to college, I also worked part time while my husband sat on his ass, and I paid a sitter to watch the kids.  Now, I understand that the grant money that I received was in my name, and that I am the one responsible, or should be.  But why can't they go after my ex-husband, who even now, is still sitting on his ass, while he collects workers compensation payments, and works under the table for cash.  Perhaps this information is entirely irrelevant, but just need to vent. 

Now, my questions are simple.  Do I have to pay these grant monies back?  Should I?  Can they sue?  What options are available to me?  I have asked for proof of these monies that they say I owe.  But so far nothing.  They keep calling every day of the week, even Saturdays at 8 in the morning.  I keep telling them that I want to have written proof. 

I honestly believed that I owed nothing.  It has been over 13 years and then out of the blue they phone and say that I have to pay within 10 days or else they would take me to court.

Does anyone have any suggestions or advise for me?