Same thing happened to me yesterday. Had a reservation for a SG 128GB 6S+ at Metrotown, drove there for an hour and a half and had to wait for 30 minutes only to be told that they didn't have it.
They were quite courteous and took my number down but I have not heard anything yet. Some explanation about how my reservation put them in a negative stock situation which is a wordy way of saying they don't have it.
I must admit there is a part of me that got a weird vibe that my phone had gone to someone else. The SG 64 and 128 seem to be by far the most difficult models to get here.