Customs clearance nightmare

We had a shipment coming in from DHL which arrived in South Africa on the 27th July 2017. Duties and vat were paid based on the amount declared. Customs stopped the shipment for inspection. I was notified to supply a commercial invoice from supplier which i gladly submitted. 10 days later i was advised that they need proof of payment which i sent. A few more days later they wanted an invoice from supplier for the freight charges which i again requested from supplier and submitted. The invoice was in a foreign language due to the supplier being foreign. I then managed to get an English version for them. A few more days later they asked why the freight charge was different. I had previously mentioned i got a discount on the shipping of 15USD less. Today i had to submit a letter stating why there was a difference which i again sent. I have customers vehicles waiting for these parts stripped in my workshop for over 2 weeks now. I am now being held liable for the costs of rental vehicles they had to get due to the 2 week delay. I do not think that DHL or customs are taking the matter seriously enough. I need the matter attended to as soon as possible.