Spam Marketing - Keep on Receiving

I keep on receiving marketing sms despite the fact that I have OPT OUT 10+ times by sms, and two times contacted the customer service contact provided on the internet page. Last time I received an email not longer than two weeks ago that I've been unsusribed yet again today I received sms. It is ******* to keep on sending messages if the customer options to unsuscribe. How difficult it can be?