Disabled phone

Hello I am needing some help. I have an iPhone XR that I purchased for my sister a year or so for my son I was able to use it for a while before he shattered the screen, I let it sit there for while until I got the funds to fix it. I finally was able to get it fixed and now the phone displays that the phone has been disabled and I try to login with my iCloud information and it will not allow it. It said to contact the previous owner which is my sister but she does not recall her old information is there anyone that could help me in this situation or guide me on this please