Misleading advertizing

Outside a petrol station there was an advertisement showing four different kinds of Royal Ice cream. There were quite  large letters saying "Royal-is, halv pris,  11 kroner". There was some text underneath and on top, with much smallet letters and not as clearly written. On top I read something about  a coffee provider.

So I went in, took an icecream from the box and gave it to the cashier, who said : 22 kroner.

But it says: half price, said I. Yes, if you buy a X coffee, it's an offer by them. Well, I paid and took it, as it was my own fault, not reading the small letters. I should have read everything. And now I noticed behind the colourful icecreams a white paper coffee mug partly hidden. 

I took a photo of the advertisement, so I could read it later, and noticed at home I had moved the camera so the white text could not be read.  When I went to take another photo later, they had just changed the advertisement! Was it deliberate, was their purpose to mislead the customer?