Free shipping? Very deceptive

I recently ordered a fly screen from Flyscreens DIY (https://magneticscreens.co.za/) and paid the full amount, under the impression that shipping is free as indicated on their website. Here, they claim that there is free delivery across all orders across South Africa. Imagine my surprise, then, when I got an email from DHL with an invoice to the amount of R304 for import tax! How exactly does this fit in to the free delivery? This is an absolutely unacceptable, and I would never have ordered if I had known that I would be paying so much for supposedly FREE shipping. This is deceptive, and very misleading advertising.