It's possible they got it from a shared list of other non-profits, but I don't know this for fact in your individual situation.
They have a mechanism to have you put on their do not call list, which is available by calling 800-472-2244 or going to www.csbps.com.
Also, if you do answer a call in the future, the blind person making the call to you can take your request to get off the calling list.
I've been donating regularly to this organization for years, and have found the interactions to always be pleasant. While the donations eventually get sold in a for-profit store (Value Village)...the prices there don't seem to get marked up as excessively as other better known donation organizations...and the margins of what goes to services for the blind seem higher than most charity organizations, according to the state website that tracks these organizations in Washington State..
I beg to differ. The people calling are not blind, they are paid fundraisers. I have asked a dozen times not to be called by these rude clowns, but of course, they never take you off any list. Been doing this for years and years. Nothing you can do about these bums. Answer and hang up.
I have asked at least 30 times to be removed from their calling list. They simply hang up. They call several times a day, then don't call for a month and then it resumes. I will soon report them to any state agency that seems relevant.