For the purposes of these rules, unless otherwise provided, 'point of taxation' shall be,-

(a) the time when the invoice for the service provided or to be provided is issued:

Provided that where the invoice is not issued within fourteen days of the completion of the provision of the service, the point of taxation shall be date of such completion.

(b) in a case, where the person providing the service, receives a payment before the time specified in clause (a), the time, when he receives such payment, to the extent of such payment.

Explanation .- For the purpose of this rule, wherever any advance by whatever name known, is received by the service provider towards the provision of taxable service, the point of taxation shall be the date of receipt of each such advance.