Instance of class not available after page_load

In the code sample below after populating the "ThisMerchant" instance of Class "Merchant" during the Page_load event, we display the page in the browser and show the "payment" and "cancel" buttons. 
When either of them is clicked and we enter that sub-routine, the contents of the "ThisMerchant" instance are gone.
Any idea why ?
 
Imports MerchantProcessing
Imports System.Web.Services
Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
 Partial Class Oltio_RequestMsIsdn
     Inherits System.Web.UI.Page
     Dim ThisMerchant As New Merchant
     Dim ThisAcquirer As New Acquirer
     Public Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not IsPostBa ...