why did apple delete all of my photos?

My iCloud Photo Library was switched off now that it’s on again all my photos and videos are gone

How long ago has it been, that you disabled iCloud Photo Library?

The photos should be staying in iCloud for a month, if you used "Disable and delete" when you signed out of iCloud Photo Library, and then they will be permanently deleted.

Have you checked the "Recently Deleted" album, if any photos are there? See: https://support.apple.com/en-in/HT205912

If you just reenabled iCloud Photo Library and you did not use the "disable and delete" option when signing out of iCloud Photo Library, the photos should still be in iCloud and you have simply to wait for them to download to your iPhone. You need to be using the same AppleID as before, and the iPhone needs to be charged and connected to the internet. Impossible, connect to a fast Wi-Fi.

While iCloud Photos Library has been disabled, did you sync your Photos to the iPhone with iTunes?

Photos synced with iTunes will be deleted from your iPhone, as soon as you enable iCloud Photo Library on a device. This e photos cannot be recovered on the iPhone.