Due to security reasons the service for usage abroad (roaming) is not activated by default for new customers until the first invoice has been paid.
I have activated the service for you manually now, so you should be able to connect within 10-15 minutes.
A restart of your phone is recommended. If you still can’t connect you might have to search for a carrier manually on your phone.
In some cases you have to attempt to connect up to 4 times before it actually establishes a connection.