WCF timeout exception: The request channel timed out while waiting for a reply

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C#

C#4.0

The request channel timed out while waiting for a reply after 00:30:00. Increase the timeout value passed to the call to Request or increase the SendTimeout value on the Binding. The time allotted to this operation may have been a portion of a longer timeout.
We have a program for uploading files,for that we created a timer.The timer elapsed event handler call the methoad for file uploading. The file uploading methoad create a proxy object and call the wcf method (proxyObject.ProcessUpload(path))
I have put a 20 files(size 40mb above),6 files has uploaded but after got exception Timeout.
we have checked the followings:
1.Increase receiveTimeout then increase the sendTimeout separately and both at the same time.
2.Then we have add" [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]" but again failed.

Sample code :
public void UploadFiles(string pdffilepath)
{
xxClient client = new xxClient();
try
{
// Prepare the files for the upload, ..
string pdfFileName = Path.GetFileNameWithoutExtension(pdffilepath));

// ..upload the files
client.Open();
client.ProcessUpload(pdffilepath);

client.Close();
}

catch (TimeoutException exception)
{ // Communication timeout

client.Abort();
throw exception;
}
}