constant disconnecting of mobile broadband

my mobile broadband keeps disconnecting at my house..
i dont understand why this is.
i first took it back to carphone warehouse when it wasn't working all, and they seemed to fix it by changing one of the settings, but i cant remember which setting they changed!
they said something about how its supposed to only be trying for 3g bands not all, but i dont know what to change to make it do that! help me!:-)

Which network is your mobile broadband with?

[Admin]

If it is a 3 Mobile Broadband connection that you have then you can change the network connection type settings as follows:

- Open up the 3 ZTE Mobile Connection software
- Click the "cog" icon on the top row of icons, its the 5th icon along.
- Click "Network Settings"
- Have "Network Selection" set to "automatic"
- Have "Mode Preferences" set to "3G-Preferred"

I hope this helps