Home Eq Servicing Corp saying we owe more than we do, mis application of funds, lost documents sacramento, California

We refinanced our loan with 1st Union in 1995 and were notified that Homeq took it over in 2000.  It is a 15 year fixed rate mortgage and we have payed every month.  We received a letter from Homeq in jan 2010 stating that the loan will reach maturity in May 2010 and we owe $12,000 - since we have paid every month and have never been 30,60,90 days late, there is no way this much could still be owed.  We have asked for a loan payment history and have only received partial history with errors and weirdly applied interest payments - we have been asking for the rest of the loan history both by phone and faxed letters and all we keep getting told is the documents are lost - they are now saying that if we do not come up with the $12K by May 10th they will forclose - any ideas, suggestions would be appreciated.  This should not be happening to folks who have payed the mortgage each month - we are not behind and never were and now have no idea what is going on or how to rectify this situation.