Hello, good day and thanks for your question. Sorry to know about this and I understand that you encountered an issue in which the refunded amount came back short instead of getting the full amount that you previously paid for.
As far as this is concerned, this should be a full refund as Microsoft will return it back from the bank or from the payment method that you have used when you made the purchase.
In this scenario, you can check it both ways in which you can check it with the bank or from the payment institution by contacting them from their support channel/s and on the other hand you can reach out to the support team with Microsoft at https://support.microsoft.com/en-us/contactus/ and then click on Windows and then click Get Home Support and then type in Billing question and click the blue button that says Sign in to contact Support and login and proceed from there (provide the refund reference) as well.