Long story short, there are very big files (like iso files-big) that were pushed into git
You should use this tool to clean your repository history:
https://rtyley.github.io/bfg-repo-cleaner/
It is the perfect tool for this kind of task
BFG Repo-Cleaner
an alternative to git-filter-branch.
The BFG is a simpler, faster alternative to git-filter-branch for cleansing bad data out of your Git repository history:
- Removing Crazy Big Files
- Removing Passwords, Credentials & other Private data
Examples (from the official site)
In all these examples bfg is an alias for java -jar bfg.jar.
# Delete all files named 'id_rsa' or 'id_dsa' :
bfg --delete-files id_{dsa,rsa} my-repo.git

After you have cleaned your repository use this tool to store your large files.
