You really need to carefully review your lease/sublease to see who is primarily responsible payment of any taxes due.
As to the amount of taxes/tax liability due, you should consult an accountant familiar with Santa Monica.
As Mr. Kane suggests, you should review the terms of the lease. From your description of your problem, it is unclear whether you are renting an apartment or commercial space in Santa Monica. In a residential lease, it is common for the property taxes to be included in the calculation of your monthly rent -- so you may already be paying for your unit's portion of the property tax due on the entire apartment building.
By comparison, commercial leases tend to be specific as to what the tenant is expected to pay. Thus, a commercial lease may be "triple-net," meaning that the tenant is expected to pay for utilities and property taxes in addition to their base rent. Understand that property taxes are assessed on the property as a whole and not individual rental units - so the landlord has to apportion the property tax bill to the individual units leased in the building. It may already be included as part of the rent, or you may get a separate bill (unlikely). In any event, your lease contract should state whether you have to pay for your unit's portion of the property tax assessed on the building.
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