It doesn't matter where you bought your phone or what sim card you are using or what location you are using it in. What does matter is the CSC code, (Consumer Software Customisation code). To find your CSC code... go to the dial pad and type in...

*#1234#

You will then get a screen showing, "Version", with 3 lines of information.

The last line, CSC, is specific to geographical region and carriers. It contains the software packages specific to that region, languages, carrier branding. if any, and also APN settings for data connection, MMS etc for your service provider.

Typically, CPW in the past, although having their own CSC code, have relied on and linked their firmware to the UK, unbranded, firmware release.

 

check this

When you do download firmwares make sure it's for GT-I9505 and the correct CSC or you will be unable to update though Samsung Kies.

 

As I thought, you are on the UK unbranded firmware and MDM, that you are on, is currently the latest for the UK. Only Samsung can tell you when that may be updated but they are pushing out the updates for Android 4.2.2 at a high rate of knots so, hopefully, fairly soon.