There is a way of preventing the same, you can register with your operator using the the DND service which will block all unsolicited calls to your phone, Most telecom operators have list like that which you can access using thier home page.
Also put your phone on silent/vibration mode so that you dont get disturbed in the middle of the night.
If the DND fails then you can Sue the the operator for breach of services, trust me 1 phone call from your side and people at the other end sit up and take notice.
After all you are the end customer and the Customer is the emperor these days.
