I have been posting here https://www.bleepingcomputer.com/forums/t/651201/routerinternet-security/#entry4287019
about my problem but it actually was somebody else's thread. I only just remembered that. Sorry.
So, this DNS Hijack is very tenacious and keeps coming back. I remove it with Zemana, but, like I said, to no avail.
So I wondered if changing DNS servers would help. And the answer is, Nope.
I change servers, and it's back. It says (how come we can't upload images anymore?) on the network graph, instead of my home network with its name it says "Multiple Networks."
I am flummoxed. Anybody has an idea?