I have received several calls from this number but have never answered them. Today I called the number back and the recording says they are the American Diebetes Association.
American Diabetes Assn. If you call them back, you get a recorded message with the option of opting out of receiving their calls. Follow the instructions on the recording.
Caller ID says "Charleston SC". They leave no message.
I call after hours (using *67 to block my number). They identify themselves as the American Diabetes Association. They wish to thank me for my previous donations and will call me again (how wonderful). They give the number to contact them directly; this number does match the phone number from the "Contact Us" section of the ADA's website. There is an option for their Do-Not-Call list (I never do this as it can actually make things worse).
I can't say that I appreciate them spoofing their caller ID.
If you are inclined to give, contact the ADA directly. That way you are not encouraging the telemarketers, and also 100% of your funds go to them (versus letting their hired-gun telemarketing firm take a substantial percentage).