So, after paying for the pro plan, we decided to stop taking in new users and reduce our usage due to an internal issue. We downgraded to the Vercel Hobby plan to cut costs, but Vercel keeps charging our card.
How can we fix this? Although we plan to upgrade again soon, this depends on when a decision is made.
Hey . I don't know what's causing this problem for your team, but we have a team of specialists with tools to investigate billing issues. Please open an Invoice Enquiry case so one of the specialists can help you figure out what's going wrong and fix the problem. 
i tried what you said but I haven’t gotten any response so far, it’s said on the mail that a shutdown is coming on the 6th, I just hope this hobby plan won’t be affected because we can’t afford to have to have downtime.