A failed render doesn't cost you anything, and it doesn't use your usage. The row in Studio tells you it ran into an issue.
Press Retry on that row. If the picture and the music both finished and only the last step was lost, the render picks up from there and uses nothing. If one of them is missing there's nothing to pick up from, so Retry takes you back to the composer and the new render uses what a new render uses. Delete clears the row if you'd rather start clean.
A render that looks frozen usually isn't. Most finish in 8–15 minutes, and a long loop or a 4K finish takes longer. If a step really has stopped, the row tells you the render ran into a problem and a Cancel render button appears. Cancelling stops the render. The parts that had already started still count against your usage, and nothing after that does.
You don't have to sit and watch for that. Chillframe checks for renders that have stopped moving, fails them for you, about 90 minutes after the render started. It waits longer for a long clip finished at a higher resolution.
One failure is usually bad luck and worth a retry. If the same brief keeps failing, email [email protected] with the video's name and roughly when it failed, and a human will read it.