If it is hard skin (a callous) then as well as rubbing off the hard skin, you will also need to apply lots of moisturiser.
The other thing it may be is a wart. Warts have roots and when they are large you would sometimes see black spots on top of them on the skin surface, but the roots do go into the flesh. If it is warts that you have, then cutting off the hard skin won't make them go away.
Make an appointment to see your doctor to get the correct diagnosis. If they are warts, the doctor can freeze them. Sometimes you may need to have more than one treatment to get rid of them.
There's never been any sort of friction. I tend to shave off the skin with a sanatized blade but then in a day or two the skin will grow back. Can someone tell me how I can cure this and why is it happening?