I think the easiest way would be to contact the Russian branch of Skype with the documents confirming the ownership of the number, and a request to provide details of calls on this number via the Skype gateway. Must provide (and there is likely to be a fake account created for this purpose).
If you do not provide, but this fellow very much zadolbali, there is still a long and difficult option: to turn to a lawyer for advice about whether to prosecute and that this is necessary. If possible, then:
— Wait for another call from this fellow and to record the conversation.
— To take the details from the operator, confirming the numerous calls.
— Fulfil other conditions.
— To inform the police about harassment/disorderly conduct.
If it's Horny, Skype will have to provide the details, and, probably, login information, ip, payment methods to Fund your account. Really guarantee what the result will be able to find this character, not (for example, if it is well entrenched: tor, a one-time card payment Yandex.Money, etc).
Here's a Cunning plan.