Did Postfinance cheat?

Some day ago Postfinance (my broker) sent me a letter saying that today they have a special "Trading Day": they will charge no commission to buy shares on SIX.

"Great, I'll take advantage and buy more shares of my usual ETF". Later on I check the receipt and see that Postfinance charged the usual commission.

I write to customer service to complain, and they reply 'you brought ETFs, not "Aktien", deal with it'. Damn!

So yes, I was stupid and didn't think that ETFs could be considered different than shares.

And yes, I was stupid to trust an ad for financial services.

But do you think they were misleading or is the fault entirely mine?

- They did not explicitly exclude ETFs.

- The fees and trading procedure for both is identical.

- And while I can see that "Aktie" and "ETF" mean different things in German, in English they write "Shares" and I would say that includes 'Shares of an ETF'.

In summary, although we are talking about small amounts I feel cheated. Was Postfinance misleading or am I entirely in the wrong?