There are some cases that DB files not showing actual size after migration even the tables and data exist, to solve this we can do the below steps:
1. Run the following command to do DB remap
# /usr/local/cpanel/bin/setupdbmap
2. Change entry in cPanel configuration file.
Open the conf file "/var/cpanel/cpanel.config"
disk_usage_include_sqldbs=1
If this parameter already there change it to 1 from 0.
3. To the last we need to update the DB cache
#/scripts/update_db_cache
Now your cPanel account will show the proper database size.