The old water will have had a teeny tiny amount of nitrogen-cycle bacteria in it (at best) - it's the filter media and gravel which have the majority of the bacteria. It's really annoying when the LFS gives bad advice, so, sympathy to you.
Transfer the old filter (media) and gravel into the new tank (you can but the gravel in a muslin bag or clean pair of old tights so you can take it out once the new gravel has been seeded with bacteria). The chances are that most (all) of the bacteria will be dead by now, but it might be better than nothing.
You could also try to get some used filter media from your LFS as this will have the good bacteria in it.
You need to do large water changes daily until the ammonia and then nitrite has fallen to zero, otherwise you risk losing the rest of your fish.