Reversal of Funds without Notification

Hello. I recently had a contract with a large airline for some software work. They had compensated me approximately $14,000 for work completed and then the contract was terminated. Both parties agreed to the termination and the termination letter was sent and dated by the airline to me. Three days after the termination was final, the the funds they had paid me for services performed were reversed out of my business account without written or verbal notice that a refund was even being requested. In fact, on the ACH form I had signed with them it indicated that notification would be sent to my email even when funds were deposited which no notification was sent. I would've considered a refund had they even asked for it, but to just withdraw money from my operating account with absolutely zero notification was quite difficult being a small business. My primary question is whether this is normal banking/business practice or not?