UPDATE
It seems I found some sort of a fix, not the best one, but still.
I’m using UPC Fibre Optics internet, and keeping in mind that I had “Network error” I tried to use some other source of internet connection. I used my mobile phone internet (Vodafone network) and broadcasted it from my phone, making it an internet access point. I then entered the game using that internet connection and suddenly I was able to buy Mercs (I was able to see prices etc…) as well as Open Cases.
Now, I’m not sure wheater or not it is down to internet provider or a router options (ports not opened?), however thanks to that I was able to finally open all of my cases. Having that said, this is still not ideal since I have to pay extra to use mobile internet…
Anyhow, I hopes that info helps in finding the source of this issue, and hopefully other people can use that knowledge.