Are your internet settings configured correctly?
See here:
http://community.48months.ie/t5/Need-Help/Internet/m-p/34493#M12560Are you sure that the new membership has started and the data allowance is available?
That will not be the case if you have a current membership which has not yet expired in which case the new membership will stack to kick in when the current one expires.
Dial *100*8# and hit call to check your data allowance balance.
If it's zero because the new membership has not started yet then you need to wait until it does or buy a data add-on.
Hope this helps.