Excess st adjustment

Hi All, '

Please advice on below mention queries:

We are a pvt ltd manufacturing co. & we have registered on as service Reciever under revrse charge method.

By mistake we have paid excess service tax i.e. 12% instead of 4% under RENT A CAB SERVICE from July-12 onward under the impression that ST has to be paid on 100% value & liabilty of service tax if the service provider is individiual n has no serv ice tax registration.

1) Can we adjust the excess service tax for future liabilty of the same service? OR

2) Can we adjust the excess service tax for future laibilty for other service also?

if yes then how to adjust this. is there any provision or notification etc.

Thanks in advance