Thanks to glitch, more than 3,500 Chicago water customers using AutoPay are billed more than once

CHICAGO (CBS) -- Check your bank account - especially if you use AutoPay for your Chicago water bill.

As CBS 2's Jermont Terry reported Tuesday night, a huge error has double- or even triple-charged customers. Late Tuesday, the city said about 3,580 AutoPay/SelectPay customers have been impacted.

The city says a technical glitch in the auto-billing is to blame – which left water customers doing double takes on their bank accounts.

One of those customers was Luis Diaz. He checks every bill – whether in the mail or online – especially his Chicago water bill.

"Every two months I get billed, I have it setup that it's automatically deducted from my account," he said.

Yet while looking over his checking account last week, the amount paid for water caused Diaz to grab his eyeglasses.

"It was actually three charges," he said.

The City of Chicago charged Diaz $186 three times. Two of the charges went through, while the third one was marked "pending" – leaving Diaz's account with a negative balance.

"It's difficult because now I've got fees," he said.

Diaz immediately called the Chicago Department of Water Management.

"I spoke with a customer rep, and she told me that she was aware that there was some issue," Diaz said. "She told me it was some kind of glitch."

Yet when CBS 2 first called the folks at City Hall, no one from the Finance Department would even acknowledge a glitch. They said they needed time to look into Diaz's overcharges – but we wanted to know how big a glitch this really was, and who else was impacted.

"This is something the city should have taken care of immediately," Diaz said, "or at least responded to you at CBS News right away."

That was last Friday. Now, three business days later, Finance Department finally acknowledged to CBS 2 "a technical error resulted in a double billing" for those who used AutoPay last week.

This was the full statement from the Finance Department:

"The Department of Finance (DOF) periodically upgrades its billing systems to make payment options more convenient for our online paying customers. In the process of upgrading our AutoPay and SelectPay features, a technical error resulted in a double billing on one day during the week of October 10th. The error was discovered and refunds were initiated the next business day."

The Finance Department will not say which day or just how much money the city overbilled.

"There's a lot of money involved, in my belief," Diaz said.

While the city claims everyone was refunded, Diaz credits his refund to one thing.

"I seriously believe the reversal wouldn't have taken place as soon as it did had you not get involved," he said.

If you pay your Chicago water bill with AutoPay, it is recommended you check your account, so as to ensure you have not been double-charged or triple-charged like Diaz was. The city is insisting the double billing issue has been fixed, but has not said what led to the problem.