Truworths won't stop spamming me

I am sick and tired of being spammed by Truworths. I have closed my account. I have contacted their call centre repeatedly. I have been into the stores. I have been assured that my number has been deleted from their system, but i keep getting sms notifications for sales and other stuff. I have blocked the number, but each time it comes from a different number so that does not help. There is no 'opt out' option in the messages. What can i do or who can i report them to? Surely this is no longer allowed?