Usually when people or especially girls go to a club, they (the club) might ask you to write your personal data such as name, address and phone no for reference and to inform u if got functions or any special promotions. Its some sort of telemarketing via sms i believe. In ur case, maybe someone gave ur hp no and  they send u all the promo sms. Maxis have nothing to do with this and u need to get the service provider to cancel ur subscription. I hope that will help.