no explanation on the outstanding amount

I was retrenched in March 2015 and was advised that there was nothing outstanding when i cancelled my membership.In September without prior communication i received a letter in the post indicating that i owe them R800.On equiry noone could explain where the amount came from.While trying to get clarity an agent from SSD called me in October and said i now owe R1200 and i explained to him that i am waiting for an explanation from Discovery and will not enter into an arrangement.Next i received an sms claiming that inhave made an arrangement with the agent and now i owe R1400.To date in a space of 2 months the amount now owed is R1600. Clearly tthe amount is increasing daiky and will end up owing thousands of rands without knowing where the amount comes from.Discovery please help with an explanation