Experienced Apple Trade-In User, Received Returned iPad 'Unavailable' Locked

I've done numerous device trade-ins over the years but I've never had Apple revise the value of the trade in to $0.00 and stating it was in activation lock. I figured 'no big deal' and that maybe I forgot to wipe the device. Either way, I planned to simply redo all the trade-in steps upon receiving it back from them, then mail it in once more for trade-in. To my surprise, when I received the iPad back from Apple it was in the 'iPad Unavailable' or locked out mode. I've since waited numerous hours, each time 8-hour increments to try to unlock the device using my last pin but the iPad remains unavailable and locked. I went a step further to try Recovery Mode but it is not being recognized by my Mac. I've never had this happen before and I don't want to speculate that someone at the FedEx store 'locked me out' by setting a passcode prior to packing and shipping it to Apple but at this point I don't know what else to do. The directions clearly state how to remove my Apple ID, turn off activation lock, erase all content, etc. and bring it in to a FedEx store for them to pack and ship. Like I mentioned, I've done this countless times before and never had this experience. Please help.