Your data is provided as an allowance with your monthly membership or a data add-on.
Cash credit on your account doesn't give you any data allowance.
It's not really clear what your problem or question is.
Do you have an active membership?
https://community.48.ie/t5/The-Knowledgebase/All-About-Memberships-and-Payments/ta-p/53105
Do you have a non zero data allowance left?
If you have used up your membership data allowance then you'll need a data add-on.
https://community.48.ie/t5/The-Knowledgebase/All-About-Add-ons/ta-p/53111
For data to work you need an active membership, a non zero data allowance and your APN configured correctly.
https://community.48.ie/t5/The-Knowledgebase/My-Internet-is-not-working/ta-p/45928
