Convert from monthly to annual plan

Hello

I am on the monthly photography plan (20GB), which I know is no longer available to new subscriptions.  I wish to switch to the annual pre-paid option (which is still available according to an article written in May 2025).  I click on manage plans and select the upgrade option to move to annual .  I get the following error message:

Error: Plan unavailable We’re unable to continue with this plan. Select another plan or if you think you’re seeing this message in error, please contact customer support.

I have tried contacting support by chat but no-one responds.  

Any ideas of how to fix this issue?

Thanks in advance for any guidance.