iPhone storage still full even after deleting 30,000+ photos and videos

Hi, I'm having issues with my iPhone storage. I have an iPhone 14 pro, and I've always had a large amount of photos and videos on my device. I have 2TB iCloud storage and usually have the "sync" option turned on so that photos on my device are regularly uploading to my iCloud, I also usually have the "optimize iPhone storage" turned on too so that lower quality versions of the photos are stored on my device with the higher quality version on iCloud. This has usually been fine - however recently my storage just keeps getting full, to the point where I'm having to delete and redownload things to make space for videos etc. I decided to back up my entire phone to iCloud, and then turn off the photo syncing and remove all photos from my device to make room. However, since doing this, my photo library has gone down from 30,000+ to 800 and the storage is still showing exactly the same? I am so confused! Can anyone help? Thanks