Need help stop Hacking

Hi,
In the last 2 weeks I have encountered two major hacking issues that I did not figure out how to solve:

1. In Google Search Console (Formerly Google Webmaster tools) I get messages about thousands of scan errors of pages that are clearly spam and return 504 and 503 response codes. It’s like someone is creating thousands of spam urls that cause the traffic usage to my website increase to crazy levels of more than 30Gb a month! This also cause my website to crush.

2. The index page title and description changes to some gibberish in Chinese.

I would appreciate any help!
Thanks,
Yon.