Bad service from Vodacom

I've been a loyal client of Vodacom for more than 20 years. I cancelled my insurance on both my contracts 14/10/2019 which is on record with them. I recieved the cancellation via email a few months ago but still got billed for it. I've been phoning every month and they promised it will get sorted out. Last month 18/3/2020 I spoke to a lady Thando that promised me that I will recieve a credit for the 6 months but guess what I got billed again this month. Now with lock down it is going to be another 2 months before it might get sorted. I really don't know what to do anymore. Is there anybody on a higher level that can assist me?