The first thing that needs to be done is to carefully read the written lease agreement that you have for your storage unit to see how the notice of the rent increase is to be mailed and received by the tenant. Meaning, is the mailing by regular postage or certfified mail, return receipt requested. In essence the terms of the contract control the obligations owed by the landlord and the tenant to the other.In your situation I would ask the landlord for a copy of the letter concerning the rent increase that you did not receive. I would take the position that your rent increase did not start until you have received the written notice of the increase.