This experience taught me that sometimes making a complaint to the correct organisation is worth the minor effort. Most people (and me in the past too) would probably just be annoyed but ignore it.
It also emboldened me to make complaints about other things, for example I complained that a local internet provider was advertising having the fastest internet in my country, even though I had internet from another provider that was 3x the speed. They did eventually change their advertising and the funny thing is that I received update letters from my local advertising authority for about two years, addressed to sone bigwig executives at Sky (who had also complained) and… me, a random nobody.
I had zero skin in that one, but felt that advertisements should have to be accurate.
As for not knowing where to send the complaints, yeah, I get it, it was something I wondered about for a while too before I decided the advertising standards authority. My reasoning was: the book was still listed on their website and on Amazon, and the blurb clearly stated that it comes with videos, so it’s part of the purchasing decision. So since it was advertised that way, it’s clearly false advertising. I took a chance and it turned out correct.
Of course not all agencies are quite so receptive or active regarding complaints so it’s hit and miss, but since you can usually do it online in a few minutes I felt it was worth five minutes of my time to try anyway. If I’d had to send a physics letter, for example, I wouldn’t have done it. My experience dealing with the advertising standards authority from the UK, though, was a very good one. They were quick and communicative.