Why let the offenders win and force you the inconvenience and cost? I've never taken the easy option against such criminals.
Let them ring and make a nuisance, report it to VM and the police. It's not your fault - let the offender pay the price for their behaviour. They will be caught.
One ex's ex thought it funny to call my mobile from his friend's landline issuing the usual playground threats, allowing me to listen to him urinating, farting and eating. I didn't hang up and kept him chatting away for over two hours. Before I went to bed I reminded him who called who, and that he called a mobile. And who was paying for the call.
He hung up immediately and didn't do it again