Welcome to just answer,
Cracked heels are also known as heel fissures.
This occur due to lack of attention to foot care rather than just overexposure or lack of moisturizing.
These are regular linear cut wounds and mostly affect the surface level which comprises of the epidermis.
Most painful is when these fissure reach dermis.
Prolonged standing, overweight, Open-back on shoes, diabetes or an underactive thyroid, psoriasis or eczema etc.
First step towards treatment is finding the cause and treating it.
At home you can try few things like soaking your feet or take a bath or shower before bed, applying a deep penetrating moisturizer, covering the foot with a moisture barrier sock and remove the dry and thick skin carefully and under supervision of medical personal.
If no effect then please visit a skin specialist as you have tried various creams best for you is to visit a doctor.
For details please visit:http://www.home-remedies-for-you.com/remedy/Cracked-Heels.html