What do you mean by "reimburse already paid challans"? Once you generate the challan, you need to deposit that particular amount (in the form of a cheque) along with 2 copies of the challan in the SBI branch and get the acknowledgment slip initially. Eventually, after the 20th of the same month, you would be able to get the acknowledged challan from the bank confirming the date of the admittance of the PF dues (by the bank) into your EPF account. You or your employer can also take a print of the remittance slip from the EPF website by opening your account.
Regards, A.B.