Firstly I would agree with a previous poster about getting this in writing, you only have NIBs sayso that AIB are reponsible, AIB may have a different opinion
In terms of complaints, you'd probably need to raise a complain via the AIB formal complaints process, you local branch should be able to give you a copy of that. Depending on how that goes, you may want to take it to the Ombudsman, however they normally won't look at a complaint until you've exhausted the complaints process with the bank in question.