I have a branch which I pulled from master branch. Let\'s call it integration.
In the integration branch, I made various commits (C1, C2, C3). When I am done, I made a
If I'm understanding your situation correct...
The main thing you're doing wrong is continuing to use a branch after it has been merged. After you merge, delete the branch. Additional work should be on a new branch.
The first "Squash and Merge" does not affect the integration branch; just how the integrated commits appear on the master branch. So, it makes sense that A, B, & C would still be there since you are reusing the old branch.
Good luck.