Galaxy S5 after System Update is asking for SIM Network Unlock PIN I recently purchased a Galaxy S5 on http://amazon.co.uk. This was a well deserved upgrade from a galaxy S2. 

When I got the phone I powered it on with my Vodafone Spain SIM card and it worked perfectly. The day after I realized that there was a system update and I ran it. As soon as the update ended the phone asked for "SIM Network Unlock PIN"

Is there any way to revert this update? is reverting the best option?

Can I unlock the phone without buying an unlock code?

I found this site http://unlockcode4u.com recommended by a friend and they seem capable of unlocking the phone, but I just expended £250 for the phone and the code is really out of my budget.

Please help.
My suggestion would be to talk to your network provider and ask them why are you seeing the above mentioned error message only after updating the firmware. Ideally it should not happen as you have bought an unlocked phone.