Held Hostage by KLM , unsafe flight plans after klm Cancel intended flight

After purchasing a Return ticket from London to Johannesburg. 12 hours before the flight klm only sends an email saying flight has changed. Not only did they extend my flight duration and instead of stopping over in Amsterdam they have changed it for a long stop over in Lagos. When rebooked with their booking team they have blatantly **** about booking the flight I was comfortable with and booked me on the unsafe flight. When re-contacting KLM they've said I need to cancel the flight which i am unwilling to take because of saftey. First their app will not let me check in and it's basically put me in a hostage situation that niether I will get a safe flight to my destination nor get compensation for they're incompetence.