What exactly happens when you try to use it?
Any error messages?
Are you absolutely sure that the two phones are unlocked for use on any network?
So no error messages?
I don't really know what you mean by a circle with a line through it.
Can you post a screenshot?
Maybe you need to order a replacement SIM and try that?
https://community.48.ie/t5/The-Knowledgebase/You-need-a-new-SIM/ta-p/8487
Edit: do you mean the symbol highlighted here?
https://androidforums.com/attachments/notification-png.149938/
Have you enabled roaming and data roaming in the phone's settings?
This is needed to access a "virtual" network such as 48.
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