Can auto insurance companies change price without new incidents?

If I entered all of my accidents/violations on my quote, bought the insurance, etc. Say I'm paying $150 a month, could the auto insurance company call me up and say I need to start paying $420 a month or they will cancel my policy?
My friend said his friend had the exact same thing happen to him. He had a violation on his record, bought his insurance, then they called him up and said they were changing it from about $150 a month to $420 a month.

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