Unwanted calls

Do you ever experience this? An unknown number calls you repeatedly and when you pick up the phone, you hear nothing?

I've been experiencing this for a while. Luckily, we are able to list a complaint and I must say the authorities take this seriously. It is not an ordinary phone number that calls. It's not a fax either. I've never seen a number like this before.

Years ago, we were also bothered by unwanted calls. My sister had a boyfriend at that time, and the calls came from his ex. She was clever enough to let the phone ring just long enough not to register the number. But one day she was a sec too late and the number turned up. I have then called back and told her plainly she should stop or I'd contact the police.

I wonder if I'll ever learn where this strange number originates from?