The basic problem behind the Error Establishing database connection is not related to WordPress and is definitely problem with the host. May be try changing the host ?
1) You can find some nice host who offer you trial
2) You can migrate everything on WordPress exactly using duplicator plugin to that host and point your dns to that host and check. Suppose you have site example.com than make testnew.example.com in the new host and point DNS through your DNS management panel to point testnew.example.com to new host ??
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