Need help soundproofing apartment

Long story short, the apartment is very badly soundproofed. I've been trying to get information from the builders, but they wont help. Neither does the real estate broker.

It's bad from both sides, theres a main house to the right and an identical apartment of mine to the left. I can hear talking, walking, music, closing cabinet doors, toilet and other bathroom activities...

Makes me feel rather uncomfortable, and as this is a grey area, I can't get refunded money from the purchase. To make things worse, several carpenters has said it's a complicated job because the bathrooms and stairs are next to each other.

I would be very grateful for any help, it would be a life changer. Could finally get a good nights sleep.

Thank you!