Charity ?

Over the christmas period I donated £10 to a cancer charity for kids from my mobile phone, since then I have had several texts asking me to donate more, then on friday morning my phone rang and a bloke with a posh voice was asking me to donate to a charity, I don't think he liked my reply and hung up without another word !

Is there not a number that you can text with the word STOP before/after it. That is the only thing with phones and the internet. I do a lot of market research and I am constantly deleting and cancelling stuff.