This is very serious, I know. We have over 15 years experience with Joomla and apparently, your website is running an older version of Joomla. It is very vulnerable. Fixing the current problem will only delay the next infection.
We are new to freelancer and if your website is not more than 20 pages, we would be willing to not only get rid of it but also create a 3.x version so that it will be secure for only $25. This is so that we can show our work and build our reputation here on Freelancer.
It will not look exactly as it looked, but that is because the current version of Joomla is responsive and its platform is different now.
Let us know what you want to do, we would be happy to do this for you. It would only take us a week, if you have 20 pages. We would build it on our server and transfer it over.
We would need the files and backups you have of the website so that we can see what it originally looked like.
Regards
Anna May