Accidentally set wrong upstream branch

How did that happen ?

I simply wanted to rename two of my git branches, local and remote. For the sake of understanding, let's say I wanted to rename the branch EVOL to DEV, and the branch DEL to DELIVERY.

To do so, I used the commands decribed here. It's quite simple. Firstly, I did, while in EVOL

git branch -m DEV
git push origin :EVOL DEV
git push origin -u DEV

Using gitk, I saw the change was effective, and did everything I wanted. So, to rename my second branch, I did the following commands (still in the now-called DEV branch)

git branch -m DEL DELIVERY
git push origin :DEL DELIVERY
git push origin -u DELIVERY

Here is where I failed. I should have done the last command in the DELIVERY branch, except I did not change, I was trying to be quick, and I didn't see the instruction on the webpage.

Consequences and problem

The DEV branch looks just like I wanted: same old EVOL branch, with a new name. However, the DELIVERY branch is just wrong, where I believe another branch was, months earlier than where DEL was. To be honest, I don't remember the use of the branch where DELIVERY is now, but ideally I would like to revert here as well whatever there was, to keep a clear history. Worse, it looks like I have lost track of my old DEL branch with its commit. I am unable to find them using gitk --all.

Since I realized my mistake, I didn't dare to try something, by fear of losing the old DEL commits. The last command I executed is that infamous git push origin -u DELIVERY

Question

Is it possible to revert that last command git push origin -u DELIVERY and/or to retrieve my commits that were on the DEL branch ?