The skype conversation could be an easy and useful solution.
Still i want to know how a bookmaker can be so sure about a double account since most IP addresses are dynamically these days.
It could happen easily you will get the IP address from somebody else in your street in a few days. So how can you be so sure it is a double account?
You can only jump to this conclusion when you undergo the KYC procedure in a strict way, then everything is solved.