Rude, threatening email out of the blue from Fedex

I'd like to add that this is not the fault of customs. It's the fault of Fedex. I've just now received a shipment via DHL and one earlier this year and did not have these problems. They sent me a link to pay the customs charges and I paid them. They asked for the import code and I provided it. Here Fedex wants the invoice and a tariff code, yet they identify the item correctly in the SMS they sent. I responded to the rep but then get a rude email the second day asking for the same things. I've dealt with FedEx late last year and there were no problems. It seems that there are particular people in this company who are very rude. I have made a complaint with the CEO of the large company in the States about FedEx SA and asked him to escalate the complaint to Fedex United States so that the local crew in SA can get some customer service lessons from head office. FedEx SA is really poor. Use DHL instead.