G'day awalker and welcome to the forum. In the first instance disconnect your wifi router, wait 30 seconds and reconnect again, then wait for a reconnection and see if that works.
If that has not fixed your problem, go to Settings>General>WiFi and tap the blue arrow next to your internet provider's name. Then tap "Forget this Network". Then go back back to WiFi and re-enter your ISPs requested info just like you did when you first set up your internet account. Let's know how you got on. Other solutions may be available.
Regards, Andrew