Maybe this helps (please ignore when done already...)
Changing from Microsoft 365 Family to Microsoft 365 Family Classic
Go to Microsoft Account, in "Subscriptions", select ""Manage"
Next screen "Switch Plan"
Select "Current Plan"
Next screen "Cancel Microsoft 365 Family" click on "Switch plan" at Microsoft 365 Family Classic
Confirm your new subscription - click [Buy]
Verifying mastercard and Confirm with your mobile
Message:
"You are playing 0.00 Eur using the card ending with NNNN" [Continue]
Pop-up "Changing your Microsoft 365 Family plan"
Next window:
You switched to Microsoft 365 Family Classic
Message:
"
Starting on [date], we’ll charge you € [amount] including estimated
VAT every year You can continue to enjoy your Microsoft 365 Family
benefits until then.
"
You will also receive an email confirmation.