I sell/repair phones for a living.
Seems that there is a possibility that the technician has basically incorrectly fixed your phone. These things happen, and in my country, such repairs are usually prefaced with “we will try and replace your battery but yada yada yada” noting that some models are not that easy to fix, especially those who use glue instead of screws.
Plus we have a rather pro consumer tribunal for problems such as these, so most of the time, we would tell the difficulty of doing those types of battery replacement.
Not sure about your country though. If you have something like a consumer tribunal, they would be a better place for you to argue things.
I always wonder why Android users have these delusions that Android has more features than iOS.
Because the truth of the matter is, features on iOS is simply better defined that the crazy world of iOS.
When you talk about iOS, 15 has more than 14 has more than 13 and so on. Rarely does a feature that existed on the previous model of iOS goes missing on the current model.
Android? Be ready for features to come and go, because now you have to factor in manufacturers, Google itself, etc etc. Notwithstanding the fact that Google has start to offer features than are behind paywalls - case in point, some extra photo editing features you need a google drive subscription to have.
And Google can always change their minds. Used to be that using google photo was an advantage since you can upload for free - that now is gone.
In the end though, I leave you with this point - When you talk about features, are you talking about the OS or the associated feature that came with specific apps - Cause we have Google apps in iOS.
Barring Apple Music, not sure what else you have from Apple in Android.