You said you're using a broadband connection too? Then try this one if it works for you:
Right click on the icon of your internet connection. (It is located on the system tray).
Then tick "Open Network and Sharing Center"
On the right side, click Change adapter settings.
Find the modem that you are using. And right click on it, then tick Properties.
Click the Configure button on General tab.
Change your maximum speed to 921600 and check all the boxes.
Click OK and you're done! Try this one. Hope it works for you now.
This wouldn't apply to me, because I'm using my broadband connection via Mobile Wi-Fi (meaning, I am connected to the device using my Wi-Fi connection), thus, I would not have this setting.
I'm still having problems updating using my broadband HSPA+ connection, even when my connection speed is going up at 2Mbps and higher. But the cable internet I'm connected to (also via my Wi-Fi connection) even at 1Mbps and below, would still complete the download.
I'm from the Philippines, and I'm using the Globe Broadband Postpaid with an HSPA+ connection that goes up to 7Mbps at night. Even at that speed, I still couldn't finish installing a Store app.