Nuisance advertising messages

For months now I have been receiving SMS messages regarding 'specials' at the Food *****s Market, Hillcrest. Since I live in Pietermaritzburg I am not interested in Hillcrest 'specials', and have never physically been into the said shop, (except to ask them to take my name of their list). So how did they get my cell number??<br> <br> Over the past few months I must have phoned the shop atleast half a dozen times, and have made a point of going into the shop three times to report the unsolicited messages. Each time I have received a luke warm response to the problem, with promises to 'see to it'.<br> I usually get 2 messages on a Saturday, and have just received one today (Monday)! Annoyingly there is no 'opt out' option with the messages. I am sick of this bombardment and wonder what on earth I can do to end these nuisance messages.