Hi, I get how stressful that can be when you just want to play and things aren’t working. What’s happening is your original account is still compromised, and the launcher is tied to that account, so even buying a second copy doesn’t fix the login issue because the launcher still sees the old credentials.
First, try signing out completely from the launcher by clicking your profile icon and choosing “Sign Out.” If you can’t access that, uninstall the launcher and reinstall it from the official Minecraft site. Then log in with the new account details you used for the second copy. If it still blocks you, it might be cached credentials, so clear your system’s Minecraft-related data or try logging in through the Microsoft Store first. Did you create the new account under a different email, and is it linked to a Microsoft account?