Worst Medical Aid - Request Cancellation

I'm trying to cancel my membership with MedShield, due to the very limited coverage their plans provide as well as the bad service they render. However, I'm not getting the plan cancelled. If I follow up they just advice me that no request was received. I have send the request more then 2 times with the termination form attached, still they didn't "receive" the request. I already joined another plan and don't want to be MedShield!!!