CHICAGO (CBS) – Several Chicago homeowners are being overcharged because of a screw-up at City Hall.

Many homeowners use special street signs discouraging motorists from blocking their driveways. Some were shocked when they saw their fees jump by hundreds of dollars, up to nearly five times what they normally paid.

CBS 2’s Pam Zekman checked it out and discovered the city apparently miscalculated the amounts.

At least 1,500 of those bills went out. Now the city is trying to figure out exactly what went wrong.

In the past, for about $100 a year property owners could get signs to help them keep their driveways clear.

It’s worked for Ronald Brumbach. But when he got a letter from the city last month, it contained a bill for his signs totaling $470 for this year.

“I said, ‘Holy smokes,’” he says.

Zekman also got one of those letters. Like others, when she called the Sign Division number listed on the communication, she was told not to worry about paying it. There had been a huge mistake.

The bills came with a notification of new rate changes. The minimum cost for a sign is $110, for up to 20 feet of curb space taken up by a driveway. For every foot after that amount, the city will charge $50 per foot.

The distance at Brumbach’s property from sign to sign is 2.5 feet more than the 20-foot minimum, so his new fee should have been $235. His bill was double that amount.

“I think that’s a big, big, big mistake,” he says.

When it’s corrected, he plans on asking the city to move one of the posts to create less distance between them, in hopes he’ll save himself some money.

Some of the residents are being undercharged for the signs.

City officials say they will send refunds to anyone who overpaid within 30 days. But they are still trying to sort out what mistakes were made and how to fix them all.

City officials say anyone who got the bills should not pay them until corrections are made.

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