Are Internet cafés, 70% of which are used for chatting with girls and listening to songs, considered permissible (halal) or forbidden (haram)? Is the owner of the café sinful for this? What is the solution to prevent these chats and songs? What is the ruling on the past profits collected before the café owner became aware of these practices?

If most of the internet users in your place commit forbidden acts, then you are not permitted to continue this work unless you can prevent them. Otherwise, you must close it down and seek a permissible source of livelihood. As for the profits generated by the shop, they are permissible if it adheres to the regulations, or if the owner of the shop is unaware of the reprehensible acts committed by the patrons.