Interest charge on a cellphone insurance premium

I have an account with Edgars and paying cellphone insurance and their service fees on a monthly basis and payments are done through my banking app and paying the correct instalments as per the sms and the statements. My challenge is that the balance keep on increasing instead of decreasing,I have not made purchases for the past six months on that account.I sent and email lodging a complaint an no response,I called in today and the explanation was not satisfactory.