How to turn off database encryption through powershell

I have setup a database which is TDE encrypted. Now I need to disable this encryption through PowerShell. I am able to get some breakthrough but facing the below error

Error:Cannot drop the database encryption key because it is currently in use. Database encryption needs to be turned off to be able to drop the database encryption key. however encryption key gets switched off but key gets dropped I believe. Below is the screenshot how it looks after first run of the code

Below  is the code that I have written/used:

   function set-EncryptionOff($ExistingDB)
{
    $ExistingDB.EncryptionEnabled=$false
    $ExistingDB.Alter();
    $ExistingDB.DatabaseEncryptionKey.Refresh()
    $ExistingDB.DatabaseEncryptionKey.Drop()

}