The problem is that the deposited funds were converted to chips and then swept by someone... You claim that it wasn't you, but that could be tricky to either prove or disprove

As LoyceV has suggested, the timestamps on the messages sent to you might be key to this... if the message was sent after the funds were swept, then it couldn't possibly be you. If it was sent before, then it's possible your mailbox has been compromised and someone else got the session key, created the chips and then swept the keys.