Ex-directory, but! how do telesales firms find your name to sell there products.?

i am ex-directory but get bombarded with tele-sales wanting to sell windows, fitted kitchens, herbal products, many more i thought this was banned in uk, where do they find your name number from, do they hack into computers to seek this information, how do you stop it, junk mali can be, where do you go about these firms that phone up 9pm, at night,