How do i center a quote, vertically and horizontally in latex?

You can also use increments of \paperheight. For instance if you wish to have the quote 1/3 down the page you can do

\vspace*{0.15\pageheight}  

\begin{quote} 
    \centering 
    quote 
\end{quote}

\newpage

Note: The multiplication factor is based on having twice the pageheight, therefore 1/3 = 0.3 . 0.3/2 = 0.15 -> 0.15\pageheight

Rather than adding a fraction of vertical space underneath it is easier to tell continuing content to start at the top of the next page with \newpage.

Try this:

\vspace*{\fill} 
\begin{quote} 
\centering 
quote 
\end{quote}
\vspace*{\fill}