How to fix Activation Error

So I am with my iphone6s (still in ios10) with a full memory storage. It starts to be lagging since this morning, and I forced a restart. It entered the activation mode right after the restart. When I tried to connect with my Wi-Fi to get it activates, it keeps show that the Wi-Fi password is incorrect (even though it is 100% correct). Tried a couples of network but still shows "Incorrect password" which causing me to stuck at the activation mode the whole day. Secondly, I even tried to connect iphone with iTunes but unfortunately iTunes shows up a message "ITunes could not connect to this IPhone, an unknown error occurred (0xE8000015)" . SOS! How should I fix this issue? Please help! Thanks.