Does not respond to customer

An inbound shipment was pre-cleared with the wrong customs code, resulting in duty being charged incorrectly. The fact was brought to Fedex's attention, by email, immediately upon receipt of the invoice, stating the correct custom codes to be used. The email was ignored for several days. Then another email arrived asking when Fedex could expect payment of their invoice. I rep**** once more to the email, stating that the original email was wrong, that I had already rep**** and that my first email had been ignored. This second email was ignored as well. A few days later, a lady from Fedex phoned to enquire about the payment, but had no idea of the history of the case. I explained once more, and she promised to look into it. No further response. A few days later, another automated email from Fedex arrived, stating that the shipment's delivery was now held up due to non-payment. Disgusted, I now phoned their call center and asked to speak to senior person to handle this issue. I eventually spoke to \Lucian\" (spelling ?) who claimed he was a team leader. The story was explained again and I was assured that a manager would call me back in due course on the same day. No further response."