You are screwed!
BUT
You can still escape......
First, I presume you mean DHL not DSL.
Second, if you don't pay the bills from DHL they will eventually re-bill to the shipper.
DHL operate like FedEx, drop and run and send the invoice later, a stupid system but perfectly legal.
If you ask me this is a shipper's money making racket.
They aren't actually smart enough for that.
My advice, just ignore the invoices and let the seller get a nice surprise in a couple of months. If you hear from the seller at that time tell them you would be perfectly happy to send them the GST amount you would have paid but not the brokerage fees.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.