Worst Network Ever

I have moved to Virgin Mobile about 4 month ago and have never encountered such pathetic network problems. I live and work in central Jhb. Everyday my phone goes off the network 3-4 times during the day, every night and morning. Whenever the battery is running low and when I plug into a charger. I have to keep restarting the phone. I have tested the sim on other phones same problem. I have taken my phone to the manufacturer they have assured me there is nothing wrong with the phone or software. I cannot believe Virgin can still run a business I'm at my ends wit I have called the call centre numerous times it fails to solve the problem and have no other option but to move to another service provider. I have been with MTN, Vodacom, CellC. And have never encountered such network issues. The worst is the phone is on and you will only know when you try to call it says not registered on network. I'm constantly assured this will be resolved to no avail.