Maersk Demands Payment Despite Proof of Payment

We cannot get in touch with Maersk, and there is absolutely no one available to address our concerns. We have paid all the charges related to our import shipment, and we have the payment receipts to prove it. Yet, Maersk continues to send us emails claiming that we still owe them money. We email them the payment receipts, but nobody reviews them. We call them, but nobody answers. We ask them to respond to our emails, but we get no response. Despite having valid proof of payment, they have even initiated enforcement proceedings against us. They sent us a notice demanding payment within three days and threatening legal action if we failed to pay. In all my years in business, I have never dealt with a company that is so incapable of keeping track of its own accounts.