I was at work and have no idea why I get these unsolicited calls - very annoying and intrusive

Rang on 3 occasions, no one spoke on other end (may be problem their end) but it was 3 different days. I understand they need to raise money but I don't think that they should be able to call "do not call" numbers like anyone else. If I want to donate, I either enter their raffles or donate to them direct....Also the fact that they always call early evening when people are sitting down to dinner, getting their kids ready for bed or trying to relax after a hard day at work, I find very intrusive.