Did you enquire from your accounts department why have they deducted the amounts?
If they are not registered in PF Act or other Act and have deducted the said amount in these heading, it is illegal.
A firm cannot deduct contributions when they are not covered under PF Act.
If incase they had once upon a time 20 workmen, they are to contribute to PF and other related accounts. In that case they should have provided you with PF Account details.
Firstly go to accounts, and
1. Ask under what heading have they deducted 1,800 from your salary?
2. Ask them to give you salary slip
3. If they say they have deducted it for PF or other things, ask them to either give you PF account no and other details or hand over the amount.
4. Is there any proof that you have been paid the said amount? Were you to sign any vouchers is cash is given to you? What amount was mentioned in the voucher?
Another thing -
Since you mentioned you're the HR for the firm, you should be knowing the formal procedures. If you wouldn't be properly educated of the rules, laws and procedures, how do you expect to do it for your staff and colleagues???
Just a piece of advice, nothing personal.