Hi,
Thank you for sharing your question. I understand about switching to Microsoft 365 Basic after canceling your current plan.
I get how annoying it is when you're trying to downgrade or change plans and the option isn't there, especially with your subscription almost up.
So, here's the deal: Microsoft doesn't let you switch plans directly once you've canceled. You can only switch while the subscription is still active. Since your current plan is good for three more days, the easiest thing to do is just buy Microsoft 365 Basic as a fresh subscription using your Microsoft account. You can do that here: https://www.microsoft.com/microsoft-365/buy/compare-all-microsoft-365-products. If you need a hand setting up the new plan or dealing with billing, hit up Microsoft Account & Billing Support at https://support.microsoft.com/contactus.
I hope this helps.
Best Regards,
Noel