I would call, and follow up with a letter, informing them that on July 1, 2009, Jane Doe had no authority to speak on behalf of your mother and that you will not be paying any bill incurred on your mother's behalf by Jane Doe on any date after 6/3/09. Ask them for confirmation, in writing. Start small, and calmly. If you don't get any action after two weeks or so, it will be time to ramp it up.

ETA: You might want to consider a suit against the former POA for squandering your mother's estate by paying bills that weren't owed. She would have owed a fiduciary duty to your mother not to do that. Just a thought, might not be worth the time and frustration.

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