See here:
We will refund, upon request, any remaining credit that you may have on your account at the point that you switch from 48 to another mobile operator. Any such request must be made within three months from the date of termination of your 48 Services agreement. Any refund is subject to an administrative fee that covers the costs incurred by 48 in meeting such a request, as published at https://48.ie/charges
You'll need to contact 48 support about this.
See the link in my signature below or email them at support@48months.zendesk.com
