When does STOP mean STOP

The constant SMS spam that I receive is outrageous. 'Please reply Y or STOP to opt out.' But no, if you reply STOP, they don't STOP. Please remove my cell number from all of your marketing SMS's. I pay close to R10,000-00 per month on insurance with Hollard for my short term insurance. Failing to remove my cell number from your marketing list will result in the following. <br> 1. I shall move my insurance with HOLLARD to another company. <br> 2. I shall answer Y to all the SMS's and create a lot of work for you just to cancel it on no 99.<br> <br> Replying STOP to your constant SMS's implies STOP. <br> <br> DO NOT SEND ME ANY MORE SMS'S. WHAT DON'T YOU UNDERSTAND BY THE WORD STOP !!!!!!