not in service sony xperia D2403 m2 aqua

I have a sony xperia D2403 aqua M2 that displays not in service when it is switched on, and a red cross appears next to the wireless network connection bars on the top right hand side.
It does not recognize the vodafone network for some reason or another! (because it is not in service i assume)
I can still connect to the internet on my home wifi, but not elsewhere!
A new sim card was put at vodafone and the red cross was still there afterwards. It was then put in another phone and it worked, which means that there could be a problem with the phone itself!
However, i then took the phone elsewhere and a random vodafone sim card was put in it and it worked. I cannot work out what the problem is! I have been told that it takes 48 hours to get the new sim activated by vodafone! is this correct?
I do not understand why the new sim card given to me by vodafone did not work on my phone, but then worked on a different phone, and then, when I went to a different shop afterwards, a random vodafone sim card was put in my phone and it worked! I am very confused to say the least! 
The different shop told me that the sim card reader was OK, because I was thinking that this was the problem, but was then told that it was not!
Everytime I put my mobile on, it comes up with the NOT IN SERVICE message on the bottom, and the red cross next to the wireless network connection bars on the top, is always there! Is there something wrong with the signal, maybe?  or is it, simply, that the new sim card from vodafone has not been activated properly yet?
 
 

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