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.