Mass add-groupmember from a CSV

Hi, 

I have a very long list of users that need to added to a group. I'm stuck. 

The script works if i have the Samaccountname. but i got the full name. Can I convert the full name to a Samaccountname?

File format is 

User,Group
test test,SG-P-Administratie Administratief medewerker
Esther Hermsen,SG-P-Administratie Administratief medewerker

So far i got this.

Import-Module ActiveDirectory
#Import CSV
$csv = @()
$csv = Import-Csv -Path "C:\Scripts\Bulk_user_group.csv"

#Loop through all items in the CSV
ForEach ($item In $csv)
{
 
      	  #add the user to the group
	  add-adgroupmember -identity $item.group -member $item.user
     Write-Host "User $($item.User) Added to $($item.group)!
}

Does anyone have a Idea on how to fix this?

I hope somebody can help me. otherwise i need to covert over 250 users manually.
There should be a solution but I can't get it to work. 

Regards Mark