can't connect to Republic of Ireland

[fixmyphone]

I live on the island of ireland and travel cross-boarder frequently. 

I used to have no trouble calling ROI from my mobile but for now some reason it wont even give me a dial up tone. How can this be fixed?  There's no reason why it shouldn't be connecting and I need to be able to make cross border calls for work. 

[Bambino]

@fixmyphone Might be a network issue or possibly a faulty sim. If you have an O2 store nearby, call in and ask them to give you a new sim. Be sure to bring photo ID with you.

How can I sort out my network issues? - o2uk

Why do I have poor coverage indoors? (o2.co.uk)

[Breanna]

Were you able to get this sorted @fixmyphone?

[pgn]

You may need to do a manual search for Irish networks, @fixmyphone - seeing the same up in the Northwest when picking up signal from Donegal. Good luck!