1) Usually we finish billing by 5th of every month, you will receive an email with information on usage for the previous month, and the information on the current balance. (ex: March invoice would contain the usage of Feb as our billing works in a way where we account the usage of the current month by the 1st of the following month)

Please note that if you have a prepaid bill plan, this is a usage summary and you will not have to pay this amount

2) You could go here  to see the payment details made by you so far: http://my.exotel.in/payments

If you're logged into your account, click on the rupee symbol on the top right corner. 

Click on Bills in the left panel. You will find a list of all your previous bills here.

3) You would have also received an email acknowledgement immediately every time after you made an online payment
. Currently, you do not receive an automated acknowledgement if you make a payment by other modes.