Can My Landlord Raise My Rent After I've Already Paid It And Force Me To Pay The Difference ( Idaho )

So to explain further my landlord was out for medical leave for two month, whoever was to cover for them never did any work. No paper works turned out no rent renewal or lease renwal anything. Cut to Dec 2 where im still under the contract of my cheaper rent. The normal landlord is back and i take my rent in and pay it on time in full. Two days later i get a notice that my rent has gone up by 100 dollars and my landlords boss is demanding i now pay the new rent. I was given no notice no warning. Is this legal? i'v been trying to fight it but the late fee's keep adding up and I'm worried by next month I'll be kicked out.