Filing a service complaint regarding an MTNL landline or broadband disruption can be accomplished by calling the dedicated customer care helpline numbers, such as dialing 1503 from an MTNL phone or contacting the respective regional consumer desks. Alternatively, subscribers can register their grievances online through the official MTNL customer service web portal by logging into their account, navigating to the fault booking or ticketing section, and submitting a detailed description of the technical issue.