Site Hacked after the install

Hello, I installed this plugin on all of my clients website and liked it how easy it was set it up. It worked great until yesterday, when I noticed some problems on 2 of my sites. A new “admin” user was created and all of my plugins were disabled. I was getting an error message: Cannot establish a database connection” even when inside the admin dashboard. I am the only admin for those sites and I didn’t create the new user. I noticed a long malware code was injected into my functions.php file. Once I deleted that code, deleted the new hacker-user and activated all the plugins, the site was back to normal. I deleted the cookie consent plugin as well, because I am not sure if the problem would occur again.
Thank you.