You wrote "I have backed it up and straight after I got iCloud ".
Perhaps there is a misunderstanding about iCloud Photos. iCloud Photos is not a backup. The purpose of iCloud Photos is a central storage in iCloud used to keep the Photos Libraries on all your devices in sync and identical. iCloud Photos is always showing on all your devices the same photos as in iCloud. If you delete photos from your iPhone they will be deleted from iCloud as well because otherwise your iCloud Photos Library would not be identical to the library on your iPhone. Even worse, when your photos are syncing with iCloud, the iCloud backup of your iPhone will no longer include the photos. The iCloud backup does not include any documents and data that are synced with iCloud. we have to make separate backups.
Could it be that you deleted photos from your iPhone, because you assumed iCloud Photos is a backup or an independent off-site storage?
If this deletion has occurred just recently, you may want to contact Apple Support asap. Perhaps the support can recover your lost photos from Apple's own backup servers. Explain, that you misunderstood how iCloud Photos is working and it is an emergency because your work depends on the photos.
See: Three Good Reasons for Using iCloud Photos Library and when not to use it - Apple Community