Stop spam calls

Called me three times today. First 2 times said they were from 02, I played along only to wind them up until they hung up on me. Third time they called the "lady" just whispered obscenities down the phone. Have been calling them back all day, every now and then they answer and I have been annoying them / playing rick Astley down the phone. Will continue to call them back and annoy them as much as possible.