Unsolicited spam SMS

I am constantly receiving spam sms's from this supplier, even after numerous attempts to block the number (they just simply use a different number) and multiple replies to STOP - clearly that option you give me is not an option at all. It is costing me money every time I am roaming and the annoyance is just too much. The company has provoked me to such an extent with their constant spam that I am now avoiding all of their stores and will continue to do so until it stops.