ABSA - personal bank info at risk

After my father's ex called him up and told him what is going on in his personal account with ABSA, about 6 month back, he went to the bank and ask the bank to investigate how is she getting his personal bank information. From there all is done and checked, as per the bank. No link from her to the account. We also stopped all bank statements been emailed to him as she might log into his emails , the passwords all has been change with the bank and personal email accounts. The Bank assure us no one goes into his account and leak information. He went back to the bank into the branch about 5 times now, and they have checked and reset and done spin reports and is at a point that they just don't know. The point is how save is our personal information with ABSA. If the bank does not email any statements to a client, all has been blocked on their system, as per the bank. As per their investigation, so called spin reports no one has been into the account. How does his ex get information and read it back to him, exactly as it is, on his current bank statement. This mean that staff can go into any account , leak the information and the bank cannot detect or will not detect this. It seem that to resolve this is to lay a complaint at the ombudsman and to move all accounts to another bank.