While importing Contact or Support Rep via CSV many customer face issue with importing getting failed
The most comman reason is that the CSV file may not have the password for the users getting imported
We have set the Display Name and Login Name as an mandatory field, but the Password field is not set as mandatory
But when there is a Login name provided then Password is by default a mandatory field
Just add the Password column in the CSV file and map it to the Password field and then try the import

Note: You may not be able to find any error trace on the CSV import failed report or error report