Sometimes clipping the nails is the only option. When I first picked up (adopted) my WW dwarf hybrid she had her Winter coat, though when she started getting her Summer coat months later I noticed how incredibly long her nails were D: they were actually curving sideways. She is such an active hamster that I never thought this would be a problem - turns out the Winter coat was protecting the nails as well as hiding them from view.
I tried everything; sandpaper, wooden/stone climbs etc. Didnt seem to work so I had to take her to the vets. I went to my local Vets4Pets and they were fantastic, it only cost £8 to get the nails cut and they were really gentle with her
I was told it was likely the nails were long when I first adopted my hamster which is why I didnt notice (plus the longer coat hid them). When they start curving like that they wont just get worn down by normal means, and having them clipped manually is the only way. She should be fine now for a few months but Im going to be keeping an eye on them!