Inphinity:michaelmurfy: There's 3 ways to stop these:
1) Reply to the message with "Stop"
2) Log into Your Telecom and turn off notifications.
3) Phone the mobile helpdesk (0800323232 prepaid, 123 postpaid) and ask them kindly to turn it off.
Thanks Michael :)
What other notifications is 2) likely to disable, though?
I believe you've got 3 in total, MBB notifications, Addon notifications and Special offers (this is off the top of my head) - You want to disable special offers and leave the other 2 active so the network can nag you to topup. The best way to ensure it's disabled is go through 1) or 3)
Edit:

You want to untick Notifications and possibly the third one.