Did you read this post?
https://community.48.ie/t5/The-Knowledgebase/iMessage-amp-Facetime-Set-Up/ta-p/53702
If so did it fail at any point?
Any error messages or other useful info?
Do calls, texts and data work ok?
If you can't get anywhere with it then you may need to contact 48 support.
See the link in my signature below.
Hope this helps.
