Service tax after tax changes from 1st april 2012

Hi All,

I have a query .

I have taken an online course from hughes education which started last year july 2011. And i have paid the full amount of the course with service tax by jan 2012.

And now the Hughes education is asking me to pay the difference of the changed service tax (last year it was 10.30% and now its 12. 36%) . As the course is yet to complete (it will be completed by sep 2012) 

As per the https://www.servicetax.gov.in/pt-of-taxtn2011.htm , the point of tax should be when payment is made and invoice is generated . For this case its jan 2012 and at that point of time it was 10.3 % and i already paid that amount.

And after giving my above justification also they are telling me to pay the amount and you can show the same to  service tax dept .

Please let me know how to proceed on this , whether hughes education is correct and i need to pay the difference .

If not what action i can take against hughes education ( any how i need to pay the excess tax difference amount , as they will not release my certificates if i dont  pay them )

Regards,

Bhaskar