critical error, website infected through the wp-file-manager

Hello everyone,

My site is a white page with a message: “There has been a critical error on your website.” I was told by the server provider (host) that my website was infected through the wp-file-manager plugin.
I struggled to solve the issue earlier and deleted the plugin, but a month later it happened again and I couldn’t restore the website which I have worked for over one year, the server provider (host) suggested that the only solution to solve (retrieve) the website is to sign up with securi security for 200 dollars to scan the site but this I couldn’t as I do not have it. I decided to look for other means of solving the problem, at least, to be able to log in to my WordPress dashboard.

My question is, as I could log into the web site’s files through Filezilla, Please, where can I find the infected files?
2. Have anyone solved such issues here, There has been a critical error on your website?
3. Are another alternative to restore my website the white page? I have given many works to the website. Please, help me if you can, Thank you