Silken Guardian

I bought an item for L$990 for a friend, The transaction text shown in open chat that the right name was found and the L$ paid to the seller and taken from my account but the 3rd party received nothing. I have sent 3 ncs with all relevant logs to the seller, now a week has past and the seller just ignores any communication from me. Surely this just cannot be acceptable. How do I get my lindens back that have effectively been dishonestly obtained? My account transaction history shows the lindens paid to the seller, all the correct keys and numbers, dates and times of the transaction etc What is my next move?