Can't get rid of whitehead patch on chin

I have been getting white patches the size ~ half an inch on my chin, which i can't get rid of for years. They are white, like whiteheads, and the area is raised. They feel hard to touch and i can't get rid of them no matter what i do. I went to see a dermatologist and he put me on Antibiotics . I discontinued the treatment after seeing no improvements for 2 months. They don't respond either to topical treatment and peels either.

I also tend to get pimples on my chin...they seem the non-inflamed type....hard with not puss or head.

I don't know what's wrong with me...why do i keep getting raised white patches and Acne on my chin? Can you help?

Thanks.