I recently had something similar happen.
I have a bestbuy.com account with a best buy RZ credit card and GCU subscription (it's also elite plus). My billing and shipping address are the same. (address "A")
My girlfriend has a bestbuy.com account with a best buy RZ credit card and GCU subscription. Her billing address and shipping address match but are different from mine (i.e. address "B")
I almost exclusively order from my account and have stuff shipped to my address (address "A"). I haven't ever gone over quantity limits on an item by placing multiple orders.
I did however order a Pip-boy edition (PS4) on both my account and her account and shipped to their respective addresses (I did not overlap billing/shipping information). I did the same with the MGS V CE as those are franchises I am really into and I wanted a sealed copy of both games.
With the MGS V CE Best Buy didn't send me a code for the CE content (manufacturer didn't pack the codes in the box). I had the contact the BB forums on both accounts and I did so from the same computer so I'm guessing maybe they tracked the IP address?
I haven't bothered contacting customer support because I know they are useless and will just repeat verbatim what you were told. I"m hoping at some point the ban will fall off but if not I've heard opening a new .com account will work.
It's just a little ridiculous to me because in the past I've ordered tens of thousands of dollars worth of stuff, sometimes to resell, and in the past year I've done very little business with Best Buy and they flagged my account over something small.