"didn't seem to point to any conclusive evidence of a high-tech digital / informational societies"
You're right. I have seen no evidence for that either (although that doesn't necessarily preclude it). But I have seen plenty of evidence of higher attainments in technologies in areas that we sometimes relegate to "magic" simply because any advanced technology appears magical to those who have no understanding of the underlying dynamics (reference "cargo cults"). Certainly our particular lines of technological development are not exclusive. As to sources, I think any open-minded investigation into how the pyramids, or some other stoneworks in Egypt and South America, were done will lead you to the conclusion that our current technology cannot account for them.

"although so far there aren't anything pointing anything close to some internet-type technology in the past"

There are pointers, however, to completely alien crystal technology and to telepathic development by peoples that we would normally consider completely non-technical. There is no reason for us to conclude yet that internet-type technology is a culminating or most desirable achievement.

I will try to look into the book you recommend this weekend. Thank you.