Automatically update combo box options?

[Mahwill]

I have three combo boxes, one for client name, one for account number and one for the carrier. When a user selects the client name I have another sheet that filters all account numbers based on this client name. I have this working but it order for the account number combo box to update, I must click on a random cell in the worksheet. Is it possible to select the client name and go directly to the account number combo box without clicking a random cell first to make it update?

Here is the code I use.

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim DropSTR As Variant 'String for values in Range
Application.CalculateFullRebuild

      Dim i As Integer

           For i = 1 To ComboBox1.ListCount
               ComboBox1.RemoveItem
           Next i
   
       DropSTR = ""

       
        For Each cell In Sheets("Client Info").Range("I2:I120")
                If cell.Value <> "" Then
                DropSTR = cell.Value
               With ComboBox1
    .AddItem DropSTR
    End With
                End If
        Next
        
        Range("I1").Value = ComboBox1.Value

End Sub

If someone could help me out with this I would really appreciate it.