Tuition payment issues

My wife is going to a university in Illinois and we recently submitted a payment through the school's online payment system. According to her school's records the payment has been accepted and processed, but the money has yet to be deducted from our checking account. We've tried to inform the school three times through phone and e-mail that the money hasn't been withdrawn from our account, and we receive the same response of "The computer says it's been paid" from the school. We've been making an honest effort to inform the school of this error. If the school is unable or unwilling to correct their mistake how long do we need to keep informing them?What is the name of your state (only U.S. law)?

Q: If the school is unable or unwilling to correct their mistake how long do we need to keep informing them?

A: Until it clears your bank.