Billed when already on annual plan

I just adjusted my billing (today is April 3) and was billed. However, previously, I had paid for a whole year, and that was up in May. I didn't want my card to be billed for another entire year in May when it was up, and I wanted to switch to month-to-month (but AFTER my year expired). Since I had paid for an annual plan, and it wasn't expired yet, I should not have been charged anything until May. So essentially, zoom has made me pay twice for April. How do I get this refunded?