Can't use If statement in Android.volley onResponse

In my android project. I'll send volley request to server to check the mobile number was exist in DB or not and the server back the response as text like: "exist" or "new"

I'm already received the response and display it in Toast

but when I try to use (IF) statement to check the text of the response variable, its doesn't work

I'm tried to type (IF) in another method, and call it from onresponse(), also don't work whats wrong here? Thanks in advance