chromecast 2 problems

[Mr.Obvious]

Hey,

Just wanted to check if anyone ever had a problem like this, and if they knew how to fix it.

The gf and I bought a chromecast 2 yesterday. But it wouldn't connect to our wifi. I went to change it at the shop, thinking it might be broken, but the new one has the same problem.
I tried activating it through my laptop and I could get to the final stage in which it has to connect to the wifi. Sadly it can't connect. It always fails. 

I wouldn't bother you guys with this, but the information you can find online and any 'helpdesk' is sorely lacking.

I'm going to try installing it and activating it through my gf's iphone instead of my laptop, because my iphone is hopelessly outdated for this kind of thing. But we already tried that once yesterday and the result was confusing at best. Plus, I'd have to call up my sister to get our shared netflix switching screens to her cellphone instead of my hp-laptop, which is a bother.

Any advice?