I suspected a few years back that my late grandmother had opened an account in my name in the early eighties and a Dublin branch of my bank (AIB) told me that an account had once been initiated for me around the time in question, but nothing lodged in it. I contacted my own branch about the matter a few times; they conducted their enquiries (or so they said) and turned up nothing. Then a year later I got a letter from this same branch saying I had a dormant account with cash in it and to do something about it - the same account about which I had been enquiring. One letter in my name was misspelled on this account, which had sent the bank officials astray, it seemed
Moral of the story: ask your own branch about the suspected account. Ask another branch. Then ask another branch. Then ask another branch. Check for misspellings of your name and various addresses and misspellings of them, too. Good luck.