How to take service tax credit on prepaid recharge-mobile

None of the mobile cos. are providing bill of prepaid mobiles. Also they used to delete their records after 3 months. Now how come we can trust that they are in real depositing the actual service tax amount, especially of Full talk time recharge.

Further, how can we take credit of such service tax, because we are not having bill & service tax no. details of co.

please guide