To expand: The infrequency of their calls resulting in that I never pick up their call & it never jumps to a voicemail so they are unable to confirm that it is a 'valid' number or not & thus don't waste time calling it so often.
Calls from this number come in, I call back and it says it is on a phone without a voicemail box, and no message is left. I am on the national no call registry. Please advise next steps I can take to stop this harrassment!