Downgrading from annual plan to monthly plan

Hi,

My account expired in July and i then decided to choose a monthly pro plan, now that i try to cancel my annual subscription it says I have unpaid dues and when I checked the invoice history there is a invoice from July 2023 to July 2024. However i was able to continue using zoom through the month of august, i can pay the monthly charges but not the annual charges.How do i go about this? Pease advise