unwanted spam messages

I have never been inside one of these stores, never given any consent but i keep on getting sms's from this store (bronkhorstspruit branch particularly). Receiving unwanted messages on a regular basis is very irritating. The fact that these messages are sent without the "opt out" option also makes it ******* above the fact that my information was used and acquired with out my consent or knowledge. Please address this issue before i take more serious steps.