Did you try the other thing I mentioned - check your provider supports 4G on the sim by going to Settings >> mobile+SIM >> SIM Settings >> Network Selection. Press search for networks, this will show a list of available networks and their connection list (2G, 3G, 4G). Make sure on your provider it shows 4G, if it doesn't, and only shows 2G & 3G, this means that 4G is not supported on the network via your SIM.
If it does show 4G in the list, try selecting another network (i.e.. roaming), this may fail, but then go back and select your network again. This is how I bumped my phone to 4G, but you need to make sure 4G is set as your highest speed before switching networks, as I've previously stated in an earlier post.
If this doesn't work, you'll most likely need to contact your carrier for support.
To be honest, it doesn't matter what firmware I'm on, which is Cyan or the software version I'm using, as 4G has been available with the 820 since it's release. And I'm in the UK.
G.