Esi & epf - relating to persons engaged on contract basis

Our Organisation(State Autonomous Body) is engaged contract with several individuals/societies for supply of huge manpower for different purposes like security services, housekeeping, data entry, facilities management services, sanitation etc.. There is no direct employment relation between our organisation & the persons engaged through our contractor. Till now we are giving the cheques for ESI, EPF cheques. The contractor with whom we have entered the agreement is now insisting us to give the ESI, EPF amount by including in the contract remuneration. Further as per relevant rules, the Principal employer has to ensure the ESI & EPF is paid properly. In this regard, please advise me on the following issues: 1. whether our organisation is a "principal employer" 2. is ESI & EPF has to be paid compulsorily through online 3. If we give the ESI & EPF to the contractor, how do we know that he has given the EPF/ESI credit to only those employees who have worked for our organisation. Regards Vishnu