The problem was that i was forwarding exchange.php to exchange after the url rewrite rules so simply the code below solved it
RewriteEngine ON
RewriteBase /
RewriteCond %{DOCUMENT_ROOT}/$1.php -f [NC]
RewriteRule ^(.+?)/?$ $1.php [L]
RewriteCond %{HTTP_HOST} !^www.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]
RewriteCond %{THE_REQUEST} s/exchange?title=([^s]*)s [NC]
RewriteRule ^ /%1 [NE,QSD,R=301]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^/]+)/?$ /exchange?title=$1 [L]
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