Unfair billing / statement & misleading info givin

I worked in the motor industry and had to leave. I was on Moto Health Care and was very happy with this medical aid. I left the motor industry and was told by Moto Health Care that if I leave the industry I have to get another medical aid and I am not allowed to stay on Moto Health Care. So I found out who else is in their group of medical aid and decided to move to Momentum Health Care . Now I am billed for savings used during the year after I was given no choice but to leave Moto Health Care. I raised the issue with them, was contacted by Metropolitan Health and now I am told I could've stayed with Moto Health Care. So why must I pay R3390.00 for their misleading information.<br>