checking whether code is running under impersonated Id in WCF - wcf

Question

We have a WCF service hosted in IIS running under Default AppPool under 'Network Service' account. At some point in the service, there is a need to read a file from a location to which Network Service account does not have access and thus we need to use an 'Administrator' account to load that file in memory.
I have tried impersonation to accomplish this and my code does not throw any exception for the Administrator credentials I pass in and I am sure the Credentials are right. But the WindowsIdentity.GetCurrent().Name still shows NT Authority\Network Service even after the call to impersonate. I am using the LogonUser Win32 call that is used by many people based on my searches. I do not have any impersonation settings in my web.config from what I can tell.
My question is whether WindowsIdentity.GetCurrent().Name is the correct way to check credentials under which the code is running at that moment. If that is true, then what am I doing wrong here.
I have tried two different ways to impersonate:
https://github.com/mj1856/SimpleImpersonation which is basically a wrapper around the win32 LogonUser method
I have also tried to add the code natively as below:
/** WindowsIdentity.GetCurrent().Name prints 'NT Authority\Network Service' **/
SafeTokenHandle safeTokenHandle;
const int logon32ProviderDefault = 0;
const int logon32LogonNewCredentials = 9; // this logon type is required to allow cross-domain (WORKGROUP -> ourDomain) authentication
// Call LogonUser to obtain a handle to an access token.
bool logonSucceeded = LogonUser("user", "domain", "password", logon32LogonNewCredentials, logon32ProviderDefault, out safeTokenHandle);
if (!logonSucceeded)
{
int ret = Marshal.GetLastWin32Error();
throw new System.ComponentModel.Win32Exception(ret);
}
using (safeTokenHandle)
{
WindowsIdentity newId = new WindowsIdentity(safeTokenHandle.DangerousGetHandle());
using (WindowsImpersonationContext impersonatedUser = newId.Impersonate())
{
/** At this point, WindowsIdentity.GetCurrent().Name STILL says NT Authority\Network Service. Shouldn't it say domain\username passed in the call to LogonUser above**/
}
}
In both of these ways, I do not get an exception for credentials, so it seems that impersonation succeeds, but it seems its not really changing the credentials to the impersonated user.