Bad business practices

I entered into a cellphone contract with Telkom mobile but to my surprise, I was in arrears when I paid my first installment . When device failed to work whilst on guarantee, I was asked to pay a consultation fee for it to be checked for repairs, and the quotation for repairing it was R4000.00. I took back my faulty without being repaired but they didn't want to release it since I refused to pay the consultation fee. Is this fair and legal.