Get caller ID on your phone and learn how to block unwanted callers. Make it clear to your mother that every call from now on in your home or hers needs to be screened. You let the machine get it unless you recognize the name AND the number (because both can be spoofed).
If you are concerned about your mother becoming the victim of a ripoff, ask her to give you information on the calls she's getting before she tries to call anyone back. Block any scam calls and report them to your state's Attorney General's Office (or the equivalent if you're outside the United States).
If necessary, you can become a co-signatory on your mother's bank accounts and work with your bank to find ways to pay her legitimate bills on time and painlessly (usually through monthly deductions for legit businesses, like her telephone provider) and maybe even put her on a bit of an allowance if need be. I realize not everyone wants to do this, but if her being ripped off is a real danger, then you'll need to (with your siblings if you have any) step in and work to protect her.
Scams which target the elderly in particular are some of the worst things. Those people should rot in hell for what they do to some of our more vulnerable citizens.