If your form did not arrive that you probably will have to call again. Something must have gone wrong, like a wrong address being noted down by the person at the other end of the line. This problem will not sort itself out. Was it SBB or SNCF you bought your ticket from?
Note that you yourself also made a mistake by booking another ticket. This you should not have done. You already had a ticket. That ticket was not cancelled, so you could use it to travel to your destination by another train, or even another route, so you should just have gone to the ticket office, and asked “how are you going to get me to Lauterbrunnen”.
Never, ever, open your wallet when the railways mess up.