Unfair - Cleaner The Vet Employee Review

I worked for this company as a cleaner for a month but was then fired due to leaving early - aka when I completed my job and had nothing left to do. I did everything I was meant to do, always asked to make sure they were happy with my cleaning and was always praised. I wasn't secretive about leaving early either. I figured leaving when the job is done is common sense - especially for a minimum wage job like a cleaner position - but apparently it violated company policy, which I simply didn't know as I never had a job before. I figured I was paid for the work I do as a cleaner, not the hours I work. I could see that making sense for a customer service role but not a cleaner position? If I can get 4 hours of work done in the span of 2 and a half I figured that'd be a good thing but evidently efficiency isn't something they care about. Instead I was apparently meant to either work at an absolute snail's pace or dawdle around until the end of my shift. I wasn't even given so much as a warning and instead I was immediately let go via a phone call. Doing something like this to someone who never even worked a job before who was still on probation and during a cost of living crisis is incredibly cruel. It's particularly infuriating as they were not without flaws themselves. Honestly this place first left a sour taste in my mouth when they forgot to put away a dead dog and instead left the deceased animal in the euthanasia room for well over an hour until I pointed it out - because it smelled horrid and I couldn't really clean anything that way. They also asked me to clean the prep room (which was not in my job description) due to being short staffed. Another thing is that while it's their job to get rid of the bins in their prep room one of the vets "sneakily" left a massive bin bag full of rubbish from said prep room at the exit, clearly thinking "ah it's fine, the cleaner will get rid of it for me". I wouldn't have had an issue with it but the least you can do is ask nicely? And I thought it was quite rude how one of the vets complained to me about the customers they were talking with because they talked "too much", which wasn't very professional. In the end my biggest issue is them claiming it was a breach of trust, implying I left early to be malicious. I simply didn't know, it was an honest mistake. Obviously I would have stayed had I known, even if it meant wasting time there doing nothing.