1) On the 1st of every month, you will receive an email with information on usage for the previous month, and the information on the current balance.
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 and 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. If you need this feature, please report it here