How to Execute Oracle Function using VB.NET

Hi
I am trying to execute a Oracle function which takes two parametes as Input and return's a varchar as output>I am trying to call the function in the similar way as we call a Stored procedure.But an Error is been thrown as

PLS-00221: 'ISCTAVAILABLE' is not a procedure or is undefined

Note:'ISCTAVAILABLE'  is my Function name

I am using the below code for executing the  function

 Public Function callStoredProc(ByVal strProcedure As String, ByVal strArguments1 As String, ByVal strArguments2 As String)
        Dim oraCmd As OracleCommand
        Dim stroutput As String
        oraCmd = New OracleCommand
        Dim oraParameter As OracleParameter
        Dim dr As OracleDataReader
        Try
            oraCmd = New OracleCommand(strProcedure, oraconn)
            oraCmd.CommandType = CommandType.StoredProcedure
            If strArguments1 <> "" Then
                oraParameter = New OracleParameter("@EID", OracleDbType.Varchar2, ParameterDirection.Input)
                oraParameter.Value = strArguments1
                oraParameter.Direction = ParameterDirection.Input
                oraCmd.Parameters.Add(oraParameter)
            End If
            If strArguments2 <> "" Then
                oraParameter = New OracleParameter("@MSG_TRACK_ID", OracleDbType.Varchar2, ParameterDirection.Input)
                oraParameter.Value = strArguments2
                oraParameter.Direction = ParameterDirection.Input
                oraCmd.Parameters.Add(oraParameter)
            End If
            oraParameter = New OracleParameter() '"MESSAGETRACKINGID", OracleDbType.Varchar2)
            oraParameter.Direction = ParameterDirection.ReturnValue

            oraCmd.ExecuteNonQuery()
            stroutput = oraParameter.Value

        Catch ex As Exception
            Throw
        End Try
        Return stroutput
    End Function

I am passing the Function name as parameter along with the Two Input Parameter.