When you say you paid €20 do you mean that you bought Don membership?
Enable data roaming if you haven't already.
Do a manual scan for networks.
What networks do you see?
If you can see 48 try to connect to it. Does it work?
If you cannot see 48 then try O2.
If that still doesn't work then make sure that you have at least 25c cash credit on your account and try turning off and on again or syncing with iTunes to see if that activates your iPhone on 48 (if that is the problem).
If necessary contact 48 support for assistance.
http://www.48months.ie/help#ask-a-48-agent
Hope this helps.
