Hi Michael, first read the lease to see if the 3rd bedroom was included as your rental. Written contracts almost always supecede verbal. Then contact an attorney. Realtors sometimes are tempted to answer legal questions... but they legally cannot. Please contact an attorney, he or she will help you ferret through all of your questions on this.
It sounds to me like you are paying for space that you cannot utilize. In my opinion, you should ask the landlord for a credit or reduction in monthly rent to adjust for the space in your apartment that they are using for storage, or ask that the items be removed so you can make use of the space. If not, the pricing should compare to other 2 bedroom rental rates.
What exactly does your lease state--as for any legal rights that you may--it's best to consider a consultation with an attorney who specializes in real estate--he/she will be your best source of advice.