The Dialog is the most unethical mobile phone company in sri lanka. So change to another.
It is the best practice in the world to seek the permission of the customer before sending messages. Even that needs to be specific like SMS video call ro voice call.
No person would like advertising calls to the phone, so if ask all will say no and they have to abandon this advertising.
In SL there is no room for ethics as the regulators are sleeping . TRC, Central Bank , consumer Authority , SEC ......
So, you have no option other than changing the service provider.