FNB Connect does not work.

I had a FNB Connect phone for several years. Unfortunately the service quality has gone downhill lately. Often people try to call me and get a message: THE NUMBER DOES NOT EXIST. When people contact me on WhatsApp it works fine, but most of the normal calls are rejected. There is no facility to leave a message or the call being diverted. It simply says the number does not exist. I tried to call my number from Skype and got the same message. This is a real issue because I run a business from home and missing calls means missing business. I want to cancel my contract with FNB because of this.