negeligance of the staff member.

I bought a phone with an account at markams and I was helped by a guy called mandla at protea glen mall, and after the purchase of a phone he asked me if I wanted insurance and I said yes and proof of documents was provided to me, I recently lost my phone and great fully knowing that I have an insurance and to my surprise when I went to store telling them that I have lost my phone and I have insurance and they said no I do not have as the insurance hasn't been taking the money from the account, but I showed them proof of agreeing that I have insurance, apparently the guy that was helping me with everything has resigned and I was assisted by a lady called lerato and tried calling the area manager but the manager was not also helping me as the customer so currently I want to take the matter forward to legal or open a case for the negligence of markarms not giving necessary training to their employees.