My phone was stolen and I'd like to reactivate the same number to a new device. Unfortunately Viber is sending the code to the lost number. Is there a way I can do that?
Simple answer, no you can't. The only ways to activate are via SMS or a call to receive the activation code and both methods require your phone number because the code will be sent to it. You are no longer in possession of the number you won't be able to activate Viber.
Your only solution is to talk with your service provider if it is possible to get your lost number back (it is possible in some countries). The process involves proving that the Sim (lost number) was yours by providing the last numbers called, received, if you bought data, what was the amount, etc.