Error establishing a database connection

I purchased ECS package with WordPress on LampUbuntu, data plan, DNS & Domain and used the 5-minute WordPress install to set up a website and all well for one month.
Now suddenly unable to reach the site with "Error establishing a database connection" message.
Alibaba Support unable or unwilling to explain in plain English how I can access my files to fix possible corrupt WPress files.
They initially suggested:  
it may cause by the config of wordpress, you can change like below:
At 291 line of ./wp-includes/class-http.php, change like below:
$request_order = apply_filters( ‘http_api_transports’, array( ‘streams’ ), $args, $url );
It means that remove characters below:
‘curl’,
My problem is I do not know how to access my WordPress installation. If I did I could repair/replace files.
I tried using FileZilla but cannot access the server.
Alibaba Support will not even answer a simple question asking if is it possible to connect by FTP or is that not possible in this scenario?!!!
Can someone please explain how to access the WordPress installation on the above package?
Alibaba Support are being no help, saying they don't provide support in such cases.
Really regretting handing over my money to Alibaba!
Hope someone can help or point me to the right resources.


Thanks
Wilf