I've tried using Vitamin E oil on it with success. I put some on, cover it with socks and go about my day, or even at night before bed (but I don't like socks in bed, so I usually hang my feet off the side of the bed to avoid getting the oil on the sheets). Try looking for a brand called Jason and get one with like 10,000 IU (I think I have a bottle that is 32,000 IU and has a little stick to with with).
From what I can tell I seem to get the cracked heels in dry weather and when I walk barefoot on the upstairs carpet - maybe it sucks the water out or something and it doesn't seem that soft.
I don't know if the Vitamin E is the real solution or the barrier it creates to keep in moisture. Either way, it worked for me! (you could also try other oils...olive, coconut, etc, but the Vit. E was thick and it seemed to work faster)
I use an ointment from a brand called Gehwol. It's a German brand. Works great. I have cracks in my heels for years, before going raw or vegan. They were caused by using wrong sandals. It remains a weak spot
There are several possibilities here. IMO, it is best to build healthy moist skin from the inside out. This starts with drinking enough water ie 2-4 quarts a day, eating enough calories starting with 2500 a day, and eat at least one mono meal of oranges a day and about 10 or more. The high vitamin C content is great for collagen and promoting strong skin.
You will probably see overall good results with the following:
Diet in a Banana Peel
Eat a primate like diet where most carbohydrates and calories come from whole raw ripe fruits supplemented with about ½-2 pounds of lettuce greens a day (not kale and spinach) and about a handful of raw nuts or seeds a day. Eat enough on a daily basis with at least 2500 calories for females and at least 3000 calories for males. Drink 2-4 quarts of water a day and pee clear. Get 8-12 hours of sleep as needed. Exercise about 30 minutes a day 5-6 days a week with at least one day off for rest and repairs. Get about 30 minutes of sunshine a day on your skin for vitamin D, mental health, eye health, and healthy bones and teeth.
For more science behind how to this diet optimally for long term success: