I made some quizzes on Canvas LMS for my HSC preparation course students and one of the question I put was:
"My name is Catherine. It is not Cathy."
As this quiz was for the polite form, the first blank should be です and for the second one, I put:
じゃありません and ではありません only as possible answers. I must have had a mental blank!
One of my students asked me why her answer, じゃないです, got marked wrong.
Of course, じゃないです and ではないです are also correct!
We have to remember there are 4 negative forms for です!