I have never used MBE to ship anything home, but I go there every time I’m in Santiago to buy bubble wrap to pack up the many liters of olive oil that I always bring home.
Until a few years ago, there were always a lot of bikes inside the store on Rua Santiago Guayaquil, not far from Plaza de Galicia. The last couple of times I was there, there were no bikes - when I asked about it, they said that their bike shipping business had gotten so big that they had to get another space for the bikes. I’m assuming that their business would suffer if there were many incidents like the one you report. I’m not doubting what you say, but you may be the victim of some very bad luck.
MBE is a franchise, so I wonder if you have been able to contact the store in Santiago directly. I assume they issued the paperwork and would be willing to help you. I’ve always found the staff to be extremely pleasant, even to a low-ticket customer like me.