No Service

I spend time in both the Netherland as well as the UK — so am switching sim cards quite often.
When I came back to NL last week and popped in my Simyo simcard I got 'No Service' status.
Assuming I'd put the wrong card in I ordered a new sim card from the website.

Just recieved the new card in the mail + activated — getting the same issue: 'No Service'
Any ideas? This something to do with my SimYo account or phone settings?

Using iPhone 4, iOS6
Carrier is set to Automatic
I've tried restarting my phone etc.
My old UK sim card works fine.

Thanks!