unless your credit is very very good, you have access to 5K or 10K on the card at 3%.  I'd assume you owe more than this on the home loan.

Best case you'd save 9-3=6% for a few months of payments, assuming the cash advance didn't get charged interest.  if 10K of credit, 6 months pay back, net saving of a few hundred dollars. 

Worse case, you miss a payment, now paying 21% + 9 % = 30% per month until you recover from this mess. With 30 % interest, you'd take years to recover, hurt credit rating, loose house.  Bottom line, to re-establish credit, build up saving to equal the amount lost - never... meaning lost opportunity of the monies used to pay 21%,  All this chaos for the potential to save a couple hundred dollars..  Not me..

I know you'd plan for success, what if you get in an accident? Lose your job? or any of a hundred reasons that 1 payment is missed,, lost in the mail...

disaster!

I'd try and refinance if rates go down, pay extra in each payment,  by paying extra the effective rate would drop from 9%..  BTW, I do this all the time,  I shop for the lowest rate around, then pay extra monthly.  If something bad happens then I could quit the extra payment, keeping my credit rating intact.