THEIR MISTAKE BUT I MUST PAY

We had a parcel sent via DHL from the UK. DHL local office erronously charged duty on their worksheet. I pointed this out to them 24 hours ago and send suppliers invoice - stating origin - which does not attract duty. This morning I receive another invoice with duty charged and when phoned, I am told that it will take 14 days to have the VOC done via customs and should I want my parcel I must pay the invoice including duty! Only once they receive the VOC can they refund the monies. My point is that this is there error and they can send me an invoice excluding the duty whilst they sort this matter out internally. THEY REFUSED TO LISTEN TO MY REASONING! Left speechless !!!!