Log into the Azure Portal and go to Virtual Machines. Under Reservations, click the View option.

 

 

 

 

Click on the reserved instance you want information about:

 

 

 

Click on the hyperlink next to Billing frequency.  The next page will show payment information.

 

 

 

Additional note

 

If you hit the Return button on the screen above you will not be able to return the RI, but it will give you information about payments, refunds, and cancelled payments (see below).