Vodacom insurance ghost calls

Since my upgrade I keep getting calls from Vodacom insurance call centre numbers, but when I answer I don't hear the individual. I have in the past indicated I don't want to take out insurance on the device as it is specified on my own insurance and thus insured.

Please for the love of God stop calling me. No, I don't want you insurance and I don't want this nuisance ghost calls anymore

I tried logging a call with the customer care department for these calls to stop as I am in meetings 80% of my day and they also call when I am on the road. They can't help me. Advises me just to block them. I can block 10 numbers and they will call from another number again and again I cannot hear the person!

Please quit calling me.