"While we are unable to provide detailed information on how we link related accounts"
I don't think it means they don't know, I think it means they can't[1] "detail", i.e. tell you.
[1] Won't, of course.
[1] Won't, of course.
If a company has such rigid internal processes that it can't come up with a way to reveal at least some information to allow a paying[0] customer to successfully defend an allegation of fraud, then that process is broken.
0 - I leave as an exercise to the reader the question of what should be done for free services.