A callous on your foot is caused by friction. The cause of the friction could be one of two things. It could be friction between one of your bones and the soft tissue of your foot or friction between your footwear and your foot.
How do you get rid of the callous? You get rid of the cause of the friction. If your bone and skin are rubbing, perhaps your foot has a biomechanical fault. This can be corrected with orthotics. If there is more than one callous on your foot, though, it is less likely the orthotic will completely get rid of your problem. Too expensive you say? Let me tell you, if you have a biomechanical fault in your foot, eventually, if you live long enough, it will become a bigger problem. It will multiply into problems in other parts of your body, perhaps in your knees, hips and back. The expense of orthotics could be the price required to save you a lot of pain, in more than just your feet.
If your footwear is rubbing on your skin and causing the callous you will need to change your footwear to something that does not rub. Yes, you may need to give away your offending footwear and buy something else. Lots of people do not like this. They don't like to think about spending money on a new pair of shoes when the old ones are not worn out. Don't be a scrooge! Your feet have done a lot of work for you and they deserve to be treated right. Face the facts, your footwear does not fit you correctly. You bought the wrong shoes. Be smart, change your shoes!
If you have diabetes, and you have a callous, you have an ulcer in waiting. You cannot afford to ignore your callous. The danger, of course, is that you could start losing your foot, or part therof, to amputation(s). See your foot care nurse. After soaking your foot rub the callous with a towel, not a pumice stone. This is because the pumice stone holds bacteria, putting you at risk of infection. After rubbing it down, apply a moisturizer. Your foot care nurse can suggest some. Do this as per the directions according to the product you use. Any product with more than 20% urea is for your heels only. A moisturizer with 25% urea can break down your good skin. A product with 20% urea, or less , is safe for your whole foot.