credit card

My 82 year old mother is being harrassed by a credit card company that she is behind with in payments. She has not used this card in over 5 years, made payments though not always regularly, and the total amount due has gone from $6000 to over $10,000. She receives only a social security check, has no property or car, and has absolutely no way of paying this bill. Multiple attempts to discuss the matter with the credit card company have been futile - they say they will accept a lower payment one month, but the next month will include the difference. Now they are threatening suit, and saying no matter what happens, she will have to repay the money. If her social security checks are free from garnishment for unsecured credit cards, what can I do to stop the harrassment? My mother's health is declining, and this is not helping. Thank you.