In case it helps any in terms of how long you might be waiting, in my case GA took about 2 weeks to write to me after they had taken my details, then I wrote back and they took a month to get back again. In another thread on this board, they took 2 weeks from the passenger's letter. Neither of these are cases quite like yours as the other poster and I both waited to hear rather than pre-empting like you did and both were about carnet issues rather than wanting to buy a ticket on the train or at the other end but even so, if they move all their correspondence at the same sort of speed, it may give you an idea. In both carnet cases, they did not prosecute (rather, issued a stern letter and charged £100 or so) but as I say, the circumstances were different so unfortunately I don't know what that implies for you.