Cenvat credit

claim on input service on which yu have already paid input service tax to yur supplier to provide main service by yu.

you cannot take cenvat credit if you are availing abatement. If not availing abatement while providing output service then you can take credit of service tax ehich you have paid on input services.

Tour operators who deals with complete holiday packages, can take abatement of upto 60% or 75% as the case may be. which means that they have to pay tax only on the remaining amount and if any assessee is taking benefit of this abatement then Cenvat credit cannot be availed.
further, if a tour operator is not claiming benefit of this abatement then he have charge servixe tax on full amount of the bill raised to customer and he can avail the benefit if tax already paid i.e. cenvat credit.