FNB unwilling to assist with a security breach.

I have had my cell number added to someone else's account and I am now able to access their cellphone banking and thus have access to their funds. I am luckily not dishonest although were I it would be possible to withdraw or even transfer from their account. I have contacted FNB at least 5 seperate times to fix this as the person is unable to bank as all his OTP pins come to my number. what is very concerning is I wonder where someone else able to access my account to would FNB be this useless is helping me a And also allow some stranger to continue to have access to my account. I will by the end of the week be lodging a complaint with the FSCA in order to have this resolved as clearly security is NOT a priority of FNB. Very disappointed. I am now being asked to move to private banking. I don't trust the company I would never upgrade. My salary etc will have to be moved sadly.