To disconnect from the internet, we use the rasapi32.dll file. First, we enumerate (loop through), all the active connections using the RasEnumConnections API call, and then call RasHangUp to disconnect. This code shows you how:

'Module Code
Public Const RAS_MAXENTRYNAME As Integer = 256
Public Const RAS_MAXDEVICETYPE As Integer = 16
Public Const RAS_MAXDEVICENAME As Integer = 128
Public Const RAS_RASCONNSIZE As Integer = 412

Public Type RasEntryName
    dwSize As Long
    szEntryName(RAS_MAXENTRYNAME) As Byte
End Type

Public Type RasConn
    dwSize As Long
    hRasConn As Long
    szEntryName(RAS_MAXENTRYNAME) As Byte
    szDeviceType(RAS_MAXDEVICETYPE) As Byte
    szDeviceName(RAS_MAXDEVICENAME) As Byte
End Type

Public Declare Function RasEnumConnections Lib _
"rasapi32.dll" Alias "RasEnumConnectionsA" (lpRasConn As _
Any, lpcb As Long, lpcConnections As Long) As Long

Public Declare Function RasHangUp Lib "rasapi32.dll" Alias _
"RasHangUpA" (ByVal hRasConn As Long) As Long
Public gstrISPName As String
Public ReturnCode As Long

Public Sub HangUp()
    Dim i As Long
    Dim lpRasConn(255) As RasConn
    Dim lpcb As Long
    Dim lpcConnections As Long
    Dim hRasConn As Long
    lpRasConn(0).dwSize = RAS_RASCONNSIZE
    lpcb = RAS_MAXENTRYNAME * lpRasConn(0).dwSize
    lpcConnections = 0
    ReturnCode = RasEnumConnections(lpRasConn(0), lpcb, _
    lpcConnections)

    If ReturnCode = ERROR_SUCCESS Then
        For i = 0 To lpcConnections - 1
            If Trim(ByteToString(lpRasConn(i).szEntryName)) = Trim(gstrISPName) Then
                hRasConn = lpRasConn(i).hRasConn
                ReturnCode = RasHangUp(ByVal hRasConn)
            End If
        Next i
    End If
End Sub

Public Function ByteToString(bytString() As Byte) As String
    Dim i As Integer
    ByteToString = ""
    i = 0
    While bytString(i) = 0&
        ByteToString = ByteToString & Chr(bytString(i))
        i = i + 1
    Wend
End Function


'Form Code
Private Sub Command1_Click()
    Call HangUp
End Sub