How to hangup after transfer?

I am having a peculiar condition. What I do is I use the VSP to make a call to one PSTN line in a different country and transfer that to other PSTN line in another country using the same VSP account.

When I transfer (using snom), I get disconnected and then I will not know whether the two parties are communicating or not and whether the connection to the VSP is hung up or not?

Any solution to verify this and in case it is not, how to hang up manually?