[Resolved]  Smscaster.com — unwanted call

I have been getting calls (when in Australia recently in the middle of the night) saying they want TO GET IN TOUCH WITH ME ABOUT "YOUR RECENT ACCOIDENT". i HAVE HAD NO ACCIDENT AND i DON'T KNOW WHERE THEY GOT MY PHONE NUMBER FROM AS IT IS ONLY DISCLOSED TO RELATIVELY FEW PEOPLE.
I HAVE TRIED TO STOP THE CALLS BUT M,Y PHONE ALWAYS SAYS failed .
How can I stop this.
Jim Gellan-Adams