Everyone hates telephone solicitation. Often, those who hate it most are the people who are making the calls, who have taken the job as their final option because it is all they could find before they get evicted or before the kids are out of food.
If you really want to do a mitzvah, simply be courteous and merciful to the charity solicitor. S/he may or may not even be making minimum wage--may even be a volunteer. Even when you can't give a dime, you are keeping someone off the unemployment rolls and providing them with bankable experience. Remind them that you are a disabled woman on a limited income and tell them that you are no longer able to donate, or you might just say "Thanks for calling, but not this time".
