/Selected network (RSA CELL C) unavailable/

My Galaxy S5 has been completely offline for the past 2 weeks. I'm not able to do anything with mobile data including receiving calls or messages. I have tried restarting the device, switching to flight mode hoping it would reboot itself, none of the networks work as well. "Selected network (RSA CELL C) unavailable". Whenever i try connecting to a network be it Vodacom or Cell C an "Unable to connect. Try later" message pops up.