My landlord got a paper from a law firm saying that they are or already has foreclosed on my apartment should I pay my rent or not?

As a tenant, you have a duty to pay rent to the landlord with whom you contracted unless and until you are appropriately notified otherwise. Notice to your landlord of the commencement of foreclosure proceedings does not absolve you of the duties under your lease. At some point, the lender will obtain a court order requiring you to pay rent to the lender. Unless you are served with such an order, or are otherwise directed to pay rent to someone other than the landlord with whom you have dealt, you pay rent to your landlord.