DO NOT DISTURB SERVICE -> Stop all promotional SMS and Call from GP
Dial *121*1101# (Free of cost) -> might take up to 72 hours to activate
Dial *121*1103# (Free of cost) -> To check the status of Do not Disturb feature
and if you are crazy and want to receive promotions dial below
Dial *121*1102# (Free of cost)
And if all this confuses you or they changed the numbers talk to their customer care from their website https://www.grameenphone.com/
Then simply click on the chat icon on the right bottom corner of the website and ask them to stop the all annoying promotional SMS. They will do it for you instantly and activate DND (Do not Disturb). As simple as that!