If you had manually assigned Dial Plan & Voice Policy and started using the Site level policy then you might want to change your Dial Plan & Voice Policy for all users to back to Automatic.
Basically from
To
Copy Powershell code below
Import-Module SkypeOnlineConnector
#Change the below pool for targeting users
$RegistrarPool = "frontend.domain.com"
$users = Get-CsUser -Filter {RegistrarPool -eq $RegistrarPool} | select DisplayName
$array = @()
foreach ($user in $users)
{
$userpolicy = get-csuser $user[0].DisplayName | select DisplayName,VoicePolicy, DialPlan
$array += $userpolicy
get-csuser $user[0].DisplayName | Grant-CsDialPlan -PolicyName ""
get-csuser $user[0].DisplayName | Grant-CsVoicePolicy -PolicyName ""
#Dialplan set
#get-csuser Firstname LastName | Grant-CsDialPlan -PolicyName ""
#VoicePolicy set
#get-csuser firstname.lastname@skype.com | Grant-CsVoicePolicy -PolicyName ""
}
$array | Export-Csv -notype -Path C:\Scripts\dialplanpolicyFinal-+$RegistrarPool+.csv
Here is a picture of the working code in PowerShell ISE you can run it from Start / Run and then type powershell ise and hit enter.

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