The ring door bell is still registered to its owner

I was the 1st owner and still the owner. I had a shared ownership with my son. Recently he has removed the device from his account, I have changed the password (and still using the same email). I have done factory reset on my device. I wanted to remove RING from my iPhone and then register as a new owner, I couldn't. Basically, I cannot use the ring door bell 2 as the message coming again and again 'this device is still registered to its owner', 'ask the owner to remove it from their account'. Any help will be appreciated