Cancellation of rental property

Can u pls advise me? I rented a space my daughter could use as a studio. Due to her teaching till quite late we found the area unsafe as well as too expensive for us. We decided to move her to more suitable premises and gave Just property a months notice. We studied the contract, which read: 20 working days notice to be given but also a reasonable penalty to be paid as we did not rent for the whole year as initially planned. The contracts stipulates a R950 fee for breach of contract as well as R1900 fee for replacement of tennant. This I was prepared for. Just property has however told me that I am still responsible for ANOTHER 2 months rent, as a "reasonable penalty fee", according to CPA, although nothing was stated in the contract. Can this be done by Just property? Please advise!