Unstable connection

Hej.

I have change the internet provider and now with the new router my son's tablet lost connection and then connect again, I don't know what to do.

The technician told me that he will give me a dinamic IP and that will work but it doesn't work, I have reseted both tablet and router, I have check which channels are more "empty", nothing work. I don't know what to do more then to send it back.