Spamming phone calls

I did quote comparisons on hippo website recently and then a gentleman phoned me like 30 minutes later. I told him he must phone the next which he did but i could not answer as i have other matters to attend to . Since then i have received about 20 calls and had to block the each one of the numbers. each time they call now and leave a voice message they dont say anything. DONT THEY GET I CANT TAKE THE CALL SND DONT WANT TO SPEAK TO THEM. This is ridiculous