(MONEY Magazine) – Q I own an investment condo in New York City. In June 2004 I paid property taxes of $999.78, which were never credited. I keep getting "balance due" notices, but I've sent my documentation to various departments and spent hours on the consumer help line. Now the city's website shows me in arrears. What can I do? --Larry Bachner, Teaneck, N.J.

ANSWER About 60% of homeowners find a meaningful error on their property taxes, reports the American Homeowners Association. The good news: 80% of those homeowners manage to get the error fixed if they fight back. You certainly tried--for nearly a year. But following the dispute instructions on the New York City finance department's website and spending all that quality time on hold waiting for hotline operators turned out to be both fruitless and frustrating.

It's a good thing you wrote when you did because after we started digging, another problem surfaced: Your 2005 tax payment had mistakenly been credited to your 2004 bill. Now it wrongly appeared that you were in arrears for 2005 and had been late paying your 2004 bill, and your payment from last year was gone with the wind.

This is the kind of glitch that keeps on glitching and requires an advocate on the inside. We reviewed your proof of payment (a copy of your bank statement that showed your account had been debited for the proper sum in June 2004). Then we called Sam Miller, an assistant commissioner at the finance department, who confirmed that the payment had been received and duly noted by some department, somewhere. Just not on the record.

"It was a mistake on our part and unacceptable," says Miller. Asking the hotline operator for a supervisor--who can investigate more complex problems--might have helped, he suggests. But for persistent problems like this one, the tax commissioner's office is often the best place for consumers with clearly documented tax problems to find real help.

The interest of $67 has been waived, and your account on the website has been updated, a signal that you are now officially okay.