Deleted photos reappearing on iPhone

I had 600 or so photos from a holiday in 2012. It seems that no matter what I do to delete them, they keep downloading to my iPhone and I get the automated email encouraging me to buy more icloud storage. The photos are deleted from my phone, from icloud photos and even the recently deleted folder in icloud photos to make sure they have gone. I can't find them anywhere else. However, once a month or so, they all download from somewhere again - this problem has happened for several years. Can anyone advise?