4.
Rule 4 of Point of Taxation Rules . Determination of point of taxation in case of change of rate of tax.-
Notwithstanding anything contained in rule 3, the point of taxation in cases where there is a change of rate of tax in respect of a service, shall be determined in the following manner, namely:-
(a) in case a taxable service has been provided before the change of rate,-
(i) where the invoice for the same has been issued and the payment received after the change of rate, the point of taxation shall be date of payment or issuing of invoice, whichever is earlier; or
(ii) where the invoice has also been issued prior to change in tax rate but the payment is received after the change of rate, the point of taxation shall be the date of issuing of invoice; or
(iii) where the payment is also received before the change of rate, but the invoice for the same has been issued after the change of rate, the point of taxation shall be the date of payment;
(b) in case a taxable service has been provided after the change of rate,-
(i) where the payment for the invoice is also made after the change in tax rate but the invoice has been issued prior to the change of tax rate, the point of taxation shall be the date of payment; or
(ii) where the invoice has been issued and the payment for the invoice received before the change of tax rate, the point of taxation shall be the date of receipt of payment or date of issuance of invoice, whichever is earlier; or
(iii) where the invoice has also been raised after the change of rate but the payment has been received before the change of rate, the point of taxation shall be date of issuing of invoice.
Now you have to look into when the Invoice has been issued as your case would fall under clause (b)(ii) or (iii).