Cell C
Bad network service

I have a cell c contract which is calling me endless problems such as
1) incoming calls going directly to voicemail wherever I am from all networks
2) Receiving sms late any after sms sent- up to 12 hours later
3) Dropping calls when received
4) Calls when received not clear
I have reported these problems on 2 occasions this year and received reference numbers but the problems have continued. I have also changed cell phones but this has not helped.