You can read the contract you have signed with the agency. It should stated very clearly on refund policy.
Normally, you need to send back the maid for a certain period of time such as 21 days and 28 days for the agency to transfer the maid.
You also need to write to the agency to tell them that you want to terminate the contract.
They should refund you within certain period of time such as one month after the contract is terminated.
Hope this helps!