I need to pay them R1500,cause i changed the plan

I received a call today around 10:02 from their call center in Durban *** spoke toa lady don't remember her name. She advised me that I owe them R1500 cause I changed their plan from classic saver to key care plus from 1 of July 2015.I advised her that I don't understand as I contributed R3041.00 every month until month end of June, she advised that I only contributed I did was R4000 for the savings and the rest was going to the hospital plan, asked her how come as I was never hospitalized from last year until know, so it means that the rest of my money went into the dirtybin.she advised that with the key care plus as well, if I don't go to hospital they will not refund me,i asked her where is it written on the book, as I also don't receive the books sometimes, she advised that it was on the contract that I signed in 2007 when I joined the medical scheme. Asked her how must I remember what I signed for in 2007, I have been with the medical aid for 8years and this is the service I get from them, she advised me that I should call client care services and they willexplain to me because she didn't call me for that. I feel that I don't have a say, I either pay or get blacklisted