"Proof?" Hell, there's not even any evidence to suggest anything like that.
Con men pick "Under the ice in Antarctica" because nobody can look there, thus you get more mileage out of the claim (i.e., sell a book for a longer period.)
Exactly the same reason we always hear about ancient civilizations now covered by the ocean (or even worse, now underground due to tectonic subduction.)
Find any place that nobody can go look, and I'll guarantee you that the fringe shysters have been on it.
Harte
Personally, I think technological civilization is a highly unlikely evolutionary development. It implies a lot of different things evolved simultaneously that are not very likely to evolve in the first place. Some means to manipulate objects (opposable thumbs) are about the only obvious evolutionary adaptation, since at every stage of evolution this path confers advantages. Complex (context-free grammar) languages, however, don't seem to fit that paradigm. There exists no intermediate complexity. It's just one big jump, and there is no obvious intermediate advantages to language. Furthermore, it may be that the kind of language humans evolved (dividing the world into nouns, verbs, adjectives, and so on) has far more to do with our drive towards technology than many may assume.
I wouldn't be at all surprised if sperm whales, for example, were pretty intelligent and that they use some kind of language. But no opposable thumbs to manipulate objects. Trapped in the ocean. Language evolved to deal with a completely different environment that may not be conducive to thinking in terms of civilization in the first place.
If the discussion were limited to human civilizations that predate the rise of civilizations we know about shortly after the end of the ice age.. it may be worth speculating. Like I said, there probably was not anything very technological here because we'd see the remains of the iron mines, and there would be obvious missing resources.
Pre-industrial civilizations before we came along.. that's a possibility, but again I think we don't really understand the probabilities of evolving the prerequisites, and I suspect those probabilities are quite low.