I strongly urge a phone call during regular business hours (in Europe). It is impossible to speculate as to what happened, but all it takes is someone typing the wrong series of keys in searching for seats to wind up cancelling a ticket.
While errors do occur on the phone, it is easy enough to stay on the phone and to reconfirm the details through a readback before terminating the call.
A suggestion: using loaded terms such as "without authorization" is the worst way to handle the call. At least to start, just explain the simple facts and ask how LH will fix the issue. How all of this occurred is irrelevant so long as the tickets are reinstated.