How do we take charge with POA with Mom who insists she's still capable of financial matters?

4th time in debit giving Grandson. My Mother has always given my 34 year old son money every time he asks. She has taken out 4 payday advances this month so he can party. this is the fourth time she has not had money for bills, medicine ect. I manage to get her back on track. i have durable power of attorney. She promises to go over bills each month but when she fails to do so and he shows up every payday i know better. Only when there is no choice but to ask me for help do i find out how bad it is. I gave up my home to be with her cancer. It's been 2 years I have no home, no future and when confronted with the problem so said get out of my life. And go where? She has no intention of stopping this. She knows she never goes without anything. I do to take care of it. I did not even have enough gas to see my Dr. and one can of tuna left for 4 days. She has her food items as always. my son comes over gets high in front of her curses at me spits on me and leaves with every dime including payday advances. She is not capable of handling her accounts anymore. Refuses to admit there is a serious problem. I think she has even cashed out her small amount of life insurance
and gave it to him. What do I do now? I am in her apartment, and disabled myself. Yet I do everything Cinderella had it better than i do. i only want the best for her. How do I take control with the durable power of attorney I have?
I have proof of many months of this conduct. Thank you