How do you deal with a family member, stealing & taking advantage of our mother? Takes her to the bank & overdrafts her acct...

I hold her new I.D. & she had her expired one but the bank continues to give her money....with the expired one???? They will not talk to me because I am not on her acct. I had her taken off my mother's acct & Power of Attorney there also. It took years to get that done. She is 91 yrs old now. Any advice? She is in denial and will not believe anything from me??? I am her care provider & son....