It's insane that it isn't illegal to take someone's money and then unilaterally change the terms of the deal after the fact. Can you imagine a customer writing new terms of service and sending it to the company and expecting it to become a binding contract if they don't immediately cancel the subscription?
At most, any changes they make should not take effect until the subscription renews, and even then, changing the terms should also end any automatic renewal because it's a new agreement.