Wii U won't play the multiplayer but internet works fine

I keep getting the error code 118-0516 but my internet ins working fine on the wii u (as the test connection is working in the image below).My modem is a TG589vn v3 with no DMZ option to enable. What should i do? I tried to solve this with the support two times but both were innefective. You guys are my last hope ;-;