ISKCON & their constant spam

Is there any way to block ISKCON from reaching out to me over phone. They are literally begging every single day to donate.. the message frequency is like twice a day. I don’t even follow them & haven’t given my number even once, yet every single day I am getting messages over WhatsApp & normal messages to donate.. I have tried my best to unsubscribe from them on WhatsApp & have even switched on my DND but they keep coming back with newer numbers. It’s so god damn irritating!! Any advice on how to tackle this?