Is it permissible to remain in a rented premise belonging to a non-Islamic insurance company if terminating the contract entails paying a large financial penalty that I cannot afford, after it became clear that dealing with such companies is impermissible?

If the questioner acts upon a fatwa (definition) of permissibility, believing it to be correct, then he is excused even if the fatwa was erroneous, and the sin falls upon the one who issued the fatwa. Commercial insurance is haram (definition) (forbidden), therefore it is not permissible to lease real estate to companies involved in it. If the lessor knows of the company's forbidden activity before the contract, then the rent is not permissible for him. However, if he does not know of its impermissibility, then he may benefit from the rent until the contract ends. If the questioner is unable to annul the contract, he must enjoin them to good and forbid them from evil, and he should not renew the contract for them. If the contract is perpetual, then it is invalid according to Sharia (definition), and the company is considered an usurper, and the lessor is entitled to a fair market rent for the period of usurpation. If the lease is invalid and the benefit has been utilized, then a fair market rent becomes due.