Hello
I am Abdal and I would be glad to help you with your question.
Turning off recurring billing for the subscription prevents you from renewing your subscription once the subscription is over.
If this option is turned on then your subscription will automatically gets renewed after the current subscription is over and your card will be debited automatically.
You can refer the below article for more information
https://support.microsoft.com/office/c7c0bc32-9744-4acf-9818-815d5c96cc59
While if you cancel subscription then it will immediately cancel your subscription and you then cannot use any of the subscription features.
You can also refer the below article to know more about cancelling of your subscription
https://support.microsoft.com/office/46e2634c-c64b-4c65-94b9-2cc9c960e91b
Yes if the subscription is cancelled within 30 days of purchase then you are eligible to get the refund. The refund is credited within 3-5 business days.
If you are facing any issue while cancelling your subscription then you need to contact live Microsoft Agent through below link who could cancel your subscription from their end and if you are eligible then you'll get the refund.
https://support.microsoft.com/en-us/home/contact
I hope this information helps.
Regards,
Abdal