Had similar problem when (4 years ago) CCard address was changed in error and without my knowledge. For 2 months my paper statements were sent to a complete stranger. (I only use online statements now)
I only found out when I applied for a passport and failed their security questions..... helluva mess that was down to me to sort out even tho' it was the Bank in error. Passport Office said either I was a fraud or a victim of ID Theft..
I did get eventually a written apology and explanation (someone was sent for re-training on how to input account numbers on keypad) free Experian Reports before change and after corrected, as the strangers address had been added, I got £'s compensation and a new Card Number.
Had to kick up a lot of fuss.