No feedback. Account wrongly billed for 10 months

I went over from a 4mbs line to a 10 mbs line in March of 2021. For 8 months after that Supersonic billed me wrong. I phoned and wrote emails month after month After my account was cleared only in October and everything corrected I got another wrong bill in Nov charging me R1411.67 for a 10mbs line that is being advertised on their site for R695 and the amount I agreed upon in my contract. Again in Dec I was billed R1411.67 for a R695 contract. After countless emails, facebook messages, instagram messages, over 35 calls over the last past months I got an e-mail back from their billing dept saying the amount of R1499 is correct for my 10mbs line. The person didn’t even know what their 10mbs fibre cost. Again I phoned logged 4 cases, facebook messages emails and I just get ‘the problem has been escalated’. No solution, no correct invoice. Nobody phones me nothing. It has been 10 months now Supersonic what else do I need to do to get my basic invoice fixed? I really do not know what to do anymore, I run an online business. What must I do to get a solution please please please please please help!