So, the first way. Ask for help to the cellular operator. It should be noted that of all known operators that provide this service only MegaFon and Skylink. The service is chargeable, but not the invoice. Other operators claim that this service is not in demand, and they don't see the point in adopting it.
The second way. Almost all modern models of cell phones already have the ability to put the phone number in the "black list".
Go to phone menu "Contacts" or "phonebook depends on phone model). Select the contact that you want to put in the "black list", then edit it.
In the popup menu select "Add phone to blacklist" and confirm the selection. Now annoying companion when dialing your number will hear the busy tone.
Two small comments: first, before to enter the number of the phone in the "black list", carefully read the user manual to your mobile, as the configuration of different models may vary; second, if you move the SIM card into another phone, the setting must be repeated.