No Signal. EVER. But ALWAYS over my limit

Every month, at the beginning of the month, I receive my allocated minutes, data and SMS's. Surprisingly by the 3rd day, All my data is finished and most of the time I have no signal. I'm struggling to understand why I never have signal but I'm always over my limit. <br> <br> I moved over from Vodacom thinking that cell c was the better service provider, I was clearly wrong