In my case, I pushed several big (> 100Mb) files and then proceeded to remove them. But they were still in the history of my repo, so I had to remove them from it as well.
What did the trick was:
bfg -b 100M # To remove all blobs from history, whose size is superior to 100Mb
git reflog expire --expire=now --all
git gc --prune=now --aggressive
Then, you need to push force on your branch:
git push origin <your_branch_name> --force
Note: bfg is a tool that can be installed on Linux and macOS using brew:
brew install bfg