What is the ruling on changing the insurance company—which paid for the injured party—to a cheaper one, knowing that insurance is mandatory?

Commercial insurance is prohibited because it involves gharar (excessive uncertainty) and gambling. However, it is permissible to engage in it when forced to do so.

An insurance company is not permitted to increase the insurance premium during the validity of the contract. Rather, any increase should occur upon its renewal, at which point the insured has the option to accept or reject. The insured is not obliged to accept an increase during the contract period, even if the contract stipulates it, because both the condition and the contract are invalid in this regard.