Rate of Service Tax for Payment of tax on Receipt basis

When the service was given and invoice was issued the Rate of tax was 12.50% but when i paid the tax( @ 12.5%) after receipt of payment then the rate was 14%. Now the service tax department was if asking for 1.5% more tax. I read that there is difference between point of taxation and payment of taxation. What i think is payment tax on receipt basis has nothing to do with point of taxation.
Please help me clarify this asap.

Also please provide section no. Rules no. Notification and other links if possible so that there can be a strong evidence to prove my point.