Did you get a brand new SIM or a replacement SIM (which should have cancelled your old one in your lost phone)?
If you got a brand new one and activated it as a new SIM then it will not be linked to your existing account/membership/credit etc.
When you scan for networks do you see 48?
Can you connect to it?
If not then are you sure that you have roaming/data roaming enabled?
What make and model of phone is it?
If it's an iPhone then there may be further complications due to the stupid way that Apple do things.
E.g. you may need cash credit on your account to pay for a UK SMS (25c) that the activation process enforced by Apple does its work.
Hope this helps.
