Verizon doesn't change your cycle date, you have to request that. The only thing that changed was everyone's due dates went back. That change happened months ago so nothing was sudden.
Proration is also a very real thing and not some Verizon conspiracy--believe it or not. If you pushed your cycle date up 10 days based on a 30 day bill cycle, that creates a bill with 40 days. You then get charged your normal bill + those days it was moved since you had service for that time.
You're not telling the entire story here. No one is randomly changing cycles, customers have to go out of their way to request those type of changes.