Hi Vijay
Thank you for your answer!
Unfortunately i didn't develop the website and i don't know what it has been done. However i think you are right because i noticed that all the old 301 redirects remind to the main domain with www-
So, according to your article, Google reasonably considers most important the "www.example.com" urls.
So i will modify all the old 301 redirects and then i will try to modify the .htaccess as you suggested.
Thank you again for your time and consideration
Have a nice day!