Topic: Online multiplayer game problem (Wii U)

Hello,I have a problem.

When I want to connect to an online-multiplayer game (like Splatoon,Mario Kart 8...) it shows me this code "Error code 118-0516".

I followed all instructions that Nintendo offered me ,but it did't worked at all.On the lucky day when I did all the steps it worked perfectly (Mario Kart 8),but after that no more luck.

I bought my Wii U used,and online multiplayer worked perfectly at the sellers home,I even tried in my friend house (same everything...it works!)

And I also need to mension that Wii U is very close to WI-FI ROUTER,signal is excellent,and all other online features (Internet browser,Youtube App,Nintendo E-Store) are working perfectly...

So is it maybe the problem with my internet provider,router or something else...

And also I can't contact Nintendo via phone,because I'm currently in Montenegro,and they don't have contact numbers for that region.