Why is Siri not responding?

Start here:--> If "Hey Siri" isn't working on your iPhone or iPad - Apple Support

If the issue persists, check if your microphone is obstructed (cover os creen protector).

If you still get no help, since your iPhone is still covered by warranty, make an appointment and have it inspected at an Apple Store or Authorized Service Provider.

Regards

Giulio

Try disabling and re-enabling "Hey Siri"

You can do this by navigating to Settings>Siri & Search

Here, toggle off "Listen for "Hey Siri""

Toggle it back on and you will be prompted to setup "Hey Siri"

Hope this works for you.