Save The Children — Harassing Calls from Save The Children

I contributed ₹300/- pm for some time to Save The Children. Later I stopped. They have recently started calling me every single day. I have clearly told them that I do not want to donate anymore but they don't stop the calls. The same people call everyday. Sometimes multiple times a day. I have not started telling them that I am going to raise a complaint against them but they still do not stop. They are literally harassing me with these calls.