Many things could have gone wrong. Not necessarily your fault. Even if it was, it is a learning experience.
If I understand correctly, you divided your plant by removing the pups. You also repotted the mother in a new pot.
After you took them out of their pots you used a knife or gently broke them apart. Then you let them sit out to callous for a day before potting.
First, if you are in the Northern Hemisphere it would have been better to wait until spring. N. Hemisphere plants are in a semi-dormant or fairly dormant state in winter. Growing very slowly, so it may not have been able to recover from the whole experience if it was dormant.
Its good you let them callous, then you potted them a day later. When you repotted them did you water right away? or did you wait a week before you did your first watering. You should wait a week. Plant roots get damaged when repotted, then damages need time to heal.
Brand new potting soil come with about 30% hydrated. This is more than enough water for your plant to live off of. Even if it is an open bag it probably is at least 20% hydrated.
If you used an open bag of soil it could have become contaminated with one or more root rot diseases that killed your plant. These diseases can attack and decimated a new plant plant very quickly. I believe your plant was exposed to one of these diseases. It could have been on your knife, under your fingernails, on the cutting board. At any point it could have made contact with your plants.
I believe it is a combination of things that happened; The wrong time of the year, not waiting long enough before watering after potting and a disease that was introduced at some point.