Filenames changing after exporting from photos.

Recently I wanted to backup my iphone photos onto my macbook.

Usually I connect it with the cable, photos opens up. I select the files, import them, then export them to the right folder and I'm done. My photos have exported and are chronologically in the folder.

Today it doesn't seem to work. After exporting they get different filenames: IMG_001, APC_002 for example.

So they are not chronologically. How can I change this? It really starts to **** me off because for some reason all my photos I had imported before and then deleted of my iphone are back on my iphone. Doubling the amount of photos on my device. I now have to delete them all again.

I could use some help here because I'm out of ideas...