Dhl International
Can't get anything right

My goods have now been in customs for a week because DHL cannot manage to get the invoice right and I'm paying the penalty in non-delivery.
I have had 3 invoices all for different amounts and was assured that the last one was 100% correct and my parcel would be released from Customs this morning!!
Guess what it's still in customs and the answer I have just received from DHL is that I have not paid the correct amount.
How difficult can it be to send me a correct invoice??