Search is your friend. Rust has been discussed literally hundreds (if not thousands) of time. Removing rust is one step. But depending how far the rust has gone, if the frame is compromised, then it is time to strip the parts for another day.

Without pics, no idea on whether you are to that point yet. And even with pics, until you strip the bike down, you often will not know for sure.

Google: oxalic acid site:bikeforums.net