rental problem with landlord

Hi,

Sorry I have to use English since my machine doesn't support Chinese input.

I subleased an apartment in early May and moved out Jul 1. After a week
I received a letter from the landlord, stating that the cost for repairing the
apartment cannot be covered by the security deposit ($550), that I have
to pay an additional $824, and that if I do not pay in time they will send
collection agents which will hurt my credit.

In my 2-month stay, I didn't do anything that would cause such damage.
They replaced the carpet of the whole 2-bdrm unit for some stains in a
small area in the bath room left by the previous renter.

I have sent the landlord a letter asking for receipts for what was done and
only got a reply repeating that the cost is heavy and I must pay what they
asked.

I have two questions
- Shall I go to small claim court for this? Any suggestions?
- What will happen if I just don't pay the amount they are asking? What can collection agents do to me?

Thanks