Sounds very weird. If you bring in an authentic bag with a lock, they really should. This was the policy from the beginning of time.
If you can go visit them in person with your bag, I am sure they will give a different answer.
They act very differently over the phone vs in-person. Many times quite inconsistent. Even if they only do this in store only, they shouldn't just refuse you like that, or at least tell you that they can help only in-person.