I am getting messages from SP28301, and each they are deducting 5 riyals from my balance, mobile no. +96508543944, I want this to be stopped as soon as possible

dear sir,

im receiving a sms from this natta service and they are deducting 5SAR/sms.
i had complained STC customer service regarding this but they said they will deactivate this service and all this was done a month ago. Again when i got this message i called STC cuatomer service and conveyed them my problem they said thay had requested the website to unsubscribe my no from their list.
But still this problem persists and im losing my money to this kind of foolish pranks and suffering.

it would be greatly helpful if u help me finding a permanent solution to this problem.