Is this legal for an apartment landlord to do?

My boyfriend and I are leasing an apartment in Tempe, AZ. However, we have moved out because there are many things around the area that have proven to be unfit to raise 2 young boys around. We're still paying rent, we still have electricity on at the apartment. The landlords have been haring us like CRAZY!! We have a co signer on our apartment and they call him almost daily. The co signer gave them permission to enter our apartment one day so that they could see for themselves that there was electricity inside still. This weekend we went over to the apartment to get my son's bike out of the storage that is not located IN the apartment, but in the carport underneath the apartment. When we entered the storage, we saw that the landlords have decided to store a refrigerator in there. Is that legal!? We have not given them permission to enter our storage, or to store anything in there. They never gave any warning that they would be entering, nor did they let us know that they would leave the fridge in there. Also, we were late paying our rent this month and instead of posting a notice about it on the apartment door, they sent a letter in the mail to the co signer. Are they not legally required to let BOTH parties know??