Legal Question in Credit and Debt Law in California

Unfortunately there are only so many phone numbers, and so many debtors. Your Mom has no legal obligation to answer the calls or to speak with anyone. Politeness does not work, any conversation will only end when Mom hangs up on them. The mail should be sent back to the post office. You could theoretically take them to court, or write them cease-and-desist letters, if you can find them -- but what is your time worth.

As Michael says she is under no obligation to tell them anything or even talk to them. She can tell them they don't live there anymore, doesn't know them, they died years ago or whatever and demand for them to stop calling her.

Hope this helps and good luck.