Icloud locked
So i have this old iphone 6, and it’s got an icloud lock. the reason i cannot unlock it is because it’s my sister’ old phone and she forgot the login, i have the phone number to verify and i have resetted the email but then it says it cannot be unlocked with that email, i have no idea what else to do, apple support doesn’t help much either since i’ve tried to contact them but since they’re busy it’s not their fault. can anyone help?
iPhone 6