Poor service and refusal to cancel medical aid

I'm tired and disgusted of spectramed this medical aid scheme has been sucking money from my mother for months and now they are refusing to cancel her medical aid.it all started when she requested them to remove me as a dependant on the medical aid for 6months they have been billing her and one of their consultant by the name of Lerato said they will investigate till today nothing has happened.She then send an email requesting them to cancel the medical aid and send her medical certificate with end date,although they acknowledge receiving her email she is still waiting and when you call them their line is poor and they never pick up.I just wanna know how difficult is it to cancel a medical aid since you have provided poor service for so long.