Merge Request acts weird

I have to follow a certain workflow for my projects. I make changes on my branch, rebase them as one commit and push my branch to the remote repo and then raise a merge request to master. A code review or a feature review happens and I need to again make changes to the existing branch on my local system, rebase it with the previous commit and push it back to the remote repo. But this can only be done if I delete the branch on remote and then push my branch with the new changes because I did a rebase. Now when I do this, the existing merge request does not update with those changes, but shows me the same old changes. Whats going on? Am I doing things correctly ?