This number is that of a call center supposedly representing many different charities at least some of which are probably legit. They will not leave messages, they call at often inconvenient times, and if you answer you may have to wait until someone responds as they have an automated dialing system.
My parents have been plagued by this operation for months so this information comes from experience. You may allow them to go through their schpeil and then ask them not to contact you again, only to be contacted by another charity represented by them.
My suggestion (and I eagerly await the opportunity to speak to a caller myself): tell them you are not interested in supporting them or any other organization using this or any other calling center and that you are hereby demanding a "cease and desist". Further calls will be recorded and turned over to your attorney who will file harassment charges against anyone and any organization they represent, charity or otherwise. Be sure to keep track of any information they give you in case you need to back up your words with legal action.