Well red flags first, Haram Tours does not seem to display a Seller of Travel registration number on its website, which is required by California law. Not a good start.
Your passport is property of the US Government, so for them to seize it without a government order is unlawful, even if you owe them money.
What can you do...
Get on the phone to them right away and ask that your passport be returned, politely always works better than shouting demands. Offer to pay shipping costs. Ask them about their Seller of Travel registration number and why it is not listed. Remind them that the passport belongs to the US Government and withholding it is unlawful.
If that fails immediately report the theft / seizure of your passport to the local police and to the federal government: Passport Services, CLASP Unit, Washington DC 20522 (1-877-487-2778).
If they failed to answer the Seller of Travel licensing question, report them via: https://sotas.doj.ca.gov/consumerComplaint.action
While you are talking with the passport services office ask about obtaining a second passport or a replacement passport on an expedited basis. But keep in mind, once your passport is reported as stolen or lost it becomes invalid, (even if found later) and expedited replacement passport can still take a few days to be issued.