BMO Harris Bank Account Or Service Complaint

BMO Harris Bank account or service department,

Checking account Making/receiving payments, sending money Texas

We had a - - walk away from us in the middle of a project. He asked for - checks from us. - in which I called - - to have cancelled - however they never cancelled the check and the fraudulant - walked away with twice the amount of money he should have taken us for. I provided a customer service rep with the check number and the amount which needed to be cancelled. To my surprise a check for $45.00 was cancelled instead of the check for $7500.00 ( check number - ). Since the following check to the fraudualnt - was also cashed, I am at a loss of $15000.00 instead of $7500.00 due to harris bank not properly canceling the first check. When I spoke with Multiple layers of management, they told me there was nothing they could do because they claim I gave them the wrong check number. They should have never allowed the $7500.00 to leave my bank account and should be liable for such a loss.