So... It's hardly the support's merit (at least my requests there), but a little over an hour ago I was finally able to regain access to my account: scammers attracted the attention of many contacts from my phone book with whom I would prefer not to contact anymore, and also delete all my subscriptions to art channels, including closed channels of my friends. Well, let this remain the worst of my problems :):
I updated the password for 2FA, checked sessions on other devices and applied some additional security measures, so now everything should be fine.
No need to delete chats anymore!

Anyway, thank you so much for your patience, help and support! I hope to be back to work tomorrow :3