" if you were indeed using unauthorized third party software to obtain the achievement in question , and you do recieve a VAC ban as a result of it, we will not be able to remove it "

Because A, Steam support simply won't admit to being able to do it and B, you cannot physically be VAC banned on a game that doesn't even use VAC. Only most Valve games and some third party games use it. DbD uses EAC and direct reports to the devs. You can cheat achievements if you want to, it will never triggered an EAC ban. A manual report could get you banned by the devs directly. It would mark your profile as having a game ban, not a VAC ban.

"if you hadn't been using third party software, and the achievement in question just happaned to appear without a date/time, it's possible htat you may have simply encountered a bug that we don't have a fix for. in either case though, we cannot help you."

" even if you didn't cheat and you get banned we won't help you "
is what ou understand from
" if you were indeed using unauthorized third party software to obtain the achievement in question , and you do recieve a VAC ban as a result of it, we will not be able to remove it "