Ruined my credit history

in 2014 i entered into a contract with apartment box to occupy a flat at John Ross House, my father signed the contract on my behalf as i was not permanently employed at the time, the contract was a one year contract from 2 ********** , in 2015 i then renewed the contract from 2 ********** and again it was a one year lease agreement. in 2016 i had decided i would move into another flat with my partner but was only going to move after March so the tenant i was staying with in 2015 than renewed the lease and signed the contract for the the lease of 2 ********** and apparently he defaulted in payments for 2 or 3 months and then decided to move out before the term agreed as to the contract, i was contacted by an employee from apartment box and i was told i had to pay this money, i tried to explain to the man that i was not the lease holder for that period and was no longer occupaying that apartment, when i went onto my trans union account yesterday 16/01/2018 to my suprise they had listed the amount owed on my name under Defaults even though the contract was not mine and i was no longer in the apartment at the time of the default in payments and i had also made the office aware when i moved out and all payments were up to date.