Getting permission denied (public key) on gitlab

My problem is that I can't push or fetch from GitLab. However, I can clone (via HTTP or via SSH). I get this error when I try to push :

Permission denied (publickey) fatal : Could not read from remote repository

From all the threads I've looked, here is what I have done :

• Set up an SSH key on my computer and added the public key to GitLab
• Done the config --global for username and email
• Cloned via SSH and via HTTP to check if it would resolve the issue
• Done the ssh -T git@gitlab.com command

If you have any insight about how to resolve my issue, it would be greatly appreciated.