Why can't you use ça est? You correct this to ça c'est.

Patricia, 

you cannot use ‘ ça est ‘ - the contraction to ‘ c’est ‘ is obligatory. 

Would need to see the whole phrase to comment on using ‘ ça c’est ‘ rather than just ‘ c’est ‘ alone. When  ‘ ça c’est ‘ is used, it is often an emphasiser, repeating the subject for clear identification, as is also done in other situations eg  ‘ Moi, je … ‘ or ‘ toi, tu ‘ . Quite common in everyday French.  

We do it English too, for example ‘ Oh that, that’s nothing special/being used tomorrow …. ‘ 

 https://www.lawlessfrench.com/expressions/cest/