As a few of my colleagues have pointed out, your issue will likely be resolved by the title company that insured your transaction. A call to them or to your broker would be your best course of action.
Every real estate transaction has several checks and balances to ensure you have "clear title" at the close of escrow. The first guard at the gate is the title company. Their role is to find and address all recorded liens and encumbrances against your home. Once done they issue a preliminary title report that is sent to all parties involved in the transaction.
Next, the real estate professional you've hired to represent you will review the title report and address all matters of title. Some of these may remain after closing, for example utility easements that allow the utility company to run wires or pipes to your house. Others will be "cleared" by being paid off at the close of escrow, for example, outstanding tax bills or loans.
Third up, your escrow officer will handle the accounting of your transaction. Among other tasks, he or she will make sure all financial liens (taxes, loans, etc) are paid in full prior to recording the grant deed that transfers ownership to you.
Lastly, your lender will have a vested interest in making sure all prior financial liens are paid in full prior to recording your new ownership. In particular tax liens, which are among the few liens that would have priority over a newly recorded 1st position home loan.
While mistakes can be made on rare occasion, it's more likely the mistake is the delinquent tax notice not the unpaid balance. If it is the title insurance you've purchased at the close of escrow is intended to resolve issues just like this.
Best of luck!
Allan S. Glass
ASG Real Estate Inc. ®
149 S. Barrington Ave, Suite #660
Los Angeles . CA 90049
Direct: 213.973.8637 (213.97.FUNDS)
CA License: 01154002
Visit Allan’s Blog: http://allanglass.featuredblog.com