Bad customer experience

Cybersmart inrtoduced a package from opernserv that is free 20Gig peak and 100 gig offpeak per month. My son had a fibre line with afrihost but due to lockdown he lost his job and it had to be disconnected. I then saw this free one and app**** got a username and WOW it worked. then when/ after the 20Gig was depleated i got disconnected can not even connect after hours. so now i asked them if it is the line because on the modem the internet light is off. i got an answer that states that there is no data but there is 50 gig offpeak. they dont answer my last emails etc .... WHAT CAN BE DONE!!!