SEO: The website faces a problem of hacking Japanese keywords. What to do?

We are currently facing a problem of hacking Japanese keywords on our website ( The problem is faced on 11-25-2019 when we receive the email that shows that someone is the new owner of the Google search console. Afterwards, our almost all URLs were converted to the Japanese language. We had to resolve the developer's website recovery, submit a new sitemap and search pages manually from the Google search console.

Our traffic decreased for 2 days and after recovery, traffic returns. Even when we write the name of our company, it does not appear on the list, but after retrieving it, it is displayed and the traffic returns.

The problem is that there are now 70-80 URLs in the Google search index that is not available in the database of our website. Some of that is below.

We removed those URLs from the search console and resubmitted the site map. I also used URL parameter tools and excluded the "? /", "Nost" parameter on 11-29-2019, 5-12-2019 but the problem is still there.

The main problem is that website traffic is back, but spam URLs are still displayed in the Google index and new spam pages are also generated and indexed on Google. Most of the spam URL traffic is from Japan.

What we can do? Provide the solution so that we can remove those search index URLs and maintain the visibility of our site. We believe that this problem also faces other sites and this solution may be useful for them.