You can report it but if it's a phone call, you're almost certainly not going to get that money back. Those hotlines do better with US-based fraudsters like car dealerships that take advantage.
To the op, you're going to need to get control of your mother's finances. Getting scammed once or twice is a bit of a rite of passage for a lot of old folks but if it's happened more than that, it's not going to get better.
It can be very difficult and somewhat heartbreaking. If you're lucky, you can work it out where where you're paying all the monthly normal expenses and giving her an allowance and letting her know that it's all her money and if she wants to spend more, just call and ask. If you're unlucky, you go through the courts which is a painful and expensive process not only for an attorney but also for the bond and payments to State appointed guardians. But it's better than letting them get scammed over and over.