Caller ID says "Haymarket VA". They leave no message.
I call back after hours (using *67 to block my number). Their message identifies them 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).
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).