It's a good practice to always have up-to-date backups of your projects/sites. This way, you can always revert back to a previous working state.
If an extension has broken your site, then remove that extension.
You can do it manually by navigating to the directories of your Joomla site, where each extension places its files.
For example in the case of Akeeba, you can manually navigate to the
/administrator/components/ and rename or remove the
com_akeeba folder, do the same for the
/components/com_akeeba and all akeeba plugins in the plugins folder.
The following resources might be helpful: How to make manual re-installation of Joomla! Core without losing extensions?
Regarding Software Liability, Warranty and Support
After following the discussion in the comments (they are deleted now) and your demands for Free Support in your question: I feel we need to give a clear perspective regarding Open Source Software, the Liability and the responsibilities of the developers and the users.
Things to keep in mind:
Software is a complex product. Many things can go wrong and there can be numerous factors that can affect its operation.
At the same time, for your particular case, it's not certain that Akeeba software was responsible for your broken site.
Nobody has forced you to use that piece of software.
When using 3rd party software, you need to be aware about the terms of using it, its license and your rights. With the majority of the software out there, and especially the Open Source and/or free provided software, the end user accepts liability for the use of it and should be pre-cautious regarding any possible damage it may cause.
Akeeba as many other similar software providers, develop open source software and provide it to the public. They offer a free version with limited features and a paid version with more features. When someone gets the paid version they opt in for the more features, pluss access to direct support from the developers.
This is the way to support the developers in developing software that is useful for you, and also to get in touch with them for possible issues you might have by using it, which is actually a promise that they will try to help you as best as possible.
It's more than clear that demanding free support for a free software makes no sense - and you knew it when you downloaded and installed the software that you won't be getting support for it - that was your choice, and you intentionally went for the free version.
Akeeba Backup is under the GNU General Public License.
Please read the Software Licence that you use.
Pay attention at 15 and 16 points. A brief summary of those 2
paragraphs: the software is provided as is and the end user is
responsible for its usage, and even a possible damage or loss of data
caused by it.