downgrading icloud storage plan

I've recently upgraded my icloud plan to 200 GB but decided to change back to the free plan of only 5 GB.

following the steps guiding on the apple support center,

after choosing to downgrade and clicking the 5 GB plan' for some reason I wasn't capable to press the "done" button to ensure the change of plan.

as for now, still having to pay for the bigger storage plan.

how can I solve this situation?