I never had any issue with paying the duty, and fully expected to do so. I do object to paying an admin fee which almost doubles the cost of the duty, because it seems to me that for DHL this is simply an additional profit stream, rather than a genuine fee for providing a service, and to the aggressive way DHL demand it. Bear in mind that I'm not their customer - the sender is; I wasn't given any opportunity to agree to their charges, (and for the record, wasn't aware of it beforehand) so there is no contract, and thus the fee is unenforceable.
DHL choose to do the customs clearance, so the cost to them of doing this, which will be minimal, should be factored in to the prices they charge for delivery - as they do, for example, with bridge toll charges. Or they could simply charge the actual cost to them. A while ago some companies were charging significant extra sums to customers paying by credit card; this is now unlawful and they can only add the actual cost to them of processing the payment.
DHL threaten action they cannot legally take; this is contrary to the law. You may think this acceptable, and challenging it semantic, but I do not.
I'm sure that every time you place an order you spend time trawling through the courier's website to discover their charges, and immediately pay any sum demanded without question. There's a word for that, but it escapes me at present. Thank you for your good wishes, but they are unnecessary. I do not often buy from overseas, but when I do my orders are usually placed with businesses who use the delivered duty prepaid method, which avoids the unpleasantness of speculative charges.