Fatal Error: Uncaught Error: call to undefined function get_plugin_data after uploading 2 blog posts(wp-shopify)

Filezilla is just an FTP client, it sounds like you have the wrong credentials to login. Either the host name, username or password is probably incorrect.

You best bet, for fast results would be to contact your host. If you are unsure about who your host is you could try a tool like this.

You should be able to disable the plugin by going to Admin > Plugins. If you don’t see a plugin menu it is likely your account isn’t an administrator account.