Strange Phone Signal

[AC Question]

I have a Nexus 5 on android 5.1.1 on the UK Three network. No problems for 18 months. For some reason the network signal dropped yesterday and I cannot connect. I tried everything - even a factory reset and no result. I tried the sim in a different phone and it worked - I tried a different sim in the Nexus 5 and it worked. For some reason the Nexus 5 has stopped working with a working Three sim card. Any thoughts?

 

[B. Diddy]

Welcome to Android Central! Did you check the APN settings to make sure it was connecting to the correct network?