Bad customer service

FedEx South Africa service has become a nightmare. I have never experienced such bad service importing with FedEx before. They send back my shipment to the shipper saying that I have not paid for customs yet, and they have never sent me the invoice. I emailed them 2 times to send me the invoice but they never rep****. one of their personnel called and advised they will investigate the matter but they have never come back to me. Now I am receiving a new parcel, paid for the customs of the new parcel sent the proof of payment and no one has rep****. They now advised the shipper that they delaying the delivery because I have not paid customs. Yet, I have paid and sent an email to change the delivery address.