I don't have any effective suggestions that can help you contact the current seller / buyer, but I'd recommend you to try making the same post in the Grassroots Motorsports forum:
https://grassrootsmotorsports.com/forum/
From what I can gather, the GRM forum has quite a wide and deep reach, and the larger pool of forum regulars mean there is a higher chance they might know what can be done on the BAT side of things.
It seems pretty shady though how BAT is actively ignoring / censoring your warning messages though. I'm not surprised, but I am disappointed.