Im asking to make simple backdrops and its not doing well, when im dont its charging me 500 credit for it now I have to by more and still didn't get the backdrop I wanted

I am wanted to make a simple video of a back screen with a mic lowering but the video generator keeps adding people and various items into my video even when asked to remove. Then it charges my 500 credits and I still dint get the video I was requesting to begin with. I lost all my credits for nothing