Autogen refusing to reimburse me with pro-rata premiums. Beware hidden conditions

I cancelled one of my cars immediately mid-month and expected a pro-rata refund but Milicent told me I cannot get a refund because I did not give 30 days notice, This is news to me, as I had gotten a refund in similar cases before.

Where in the policy does it say we need 30 days notice. Also why didnt the agent advise me of this, so that I could decide..? This prompted me to cancel even the remaining vehicle, because Autogen is not the same anymore and I had trusted many years.