I'm extremely frustrated, to say the least

I'm extremely frustrated, to say the least. Initially, they wanted to take my instalment earlier, but I requested they keep the original date as I'm only paid on the last day of the month, although it's December. This morning, I woke up to find they took the instalment anyway. What if I didn't have sufficient funds in my account? The inconvenience this has caused is significant. Why couldn't they simply assist me and be honest about changing the date? It would've been much appreciated.