Dear Rajeev,
i understood that you hired buses. Under notification no. 26/2012 after, 1.10.2014 abatement is available on the services by way of renting of motor cab a bus is certainly not a motor cab, As per motor vehicles Act, a motor cab is a motor vehicle having carrying capacity not more than six passengers excluding driver. It is common knowledge that a bus certainly have carrying capacity more than six passengers. so no abatement on that after. 10.2014.
if your SP claimed abatement under 26/2012 (even though he is providing services by using buses) he is doing it wrong. your service provider has to raise an invoice without claiming abatement.
when your service provider raise invoice without claiming abatement you can not have the benefit of entry 7(a) of 30/2012 as amended you have to go under 7 (b) where both SP and SR shall pay tax to government to the extent of 50% each w.e.f 10.10.2014.
you can take the credit of tax paid by you.