Supersonic Robbing Me Blind

I have absolutely no issues with my broadband services from Supersonic, but their finance department (billing and collections) employs the most ***********, non caring and non customer focused people I've had to deal with. Here's my story: I took a subscription for a 20x2 Mb broadband subscription with 4 plumes for my mesh network at home. All was going well until I decided to upgrade the service to a 50x5 Mb service. Then suddenly in September 2020, I received an invoice for R1902,19. Upon investigation, I realised that I'm being suddenly billed for 16 Plumes instead of 4. I queried the matter with Supersonic and was promised a credit (I have an email from them to that effect) for the extra charges. I was then credited R76,94 which is way short of the extra charges that were levied on my account. Instead of R1179, I'm being invoiced R1778.97. Every month after that, my invoice has been coming with these additional charges and every month since then, till now, I've been disputing these additional charges with them. Needless to say, after 8 months since I started with this query, I'm still not close to winning this battle. There is no resolution in sight. Adding salt to my wound, they've again gone ahead and credited my account with a measly R65,97. The balance of my account currently stands at R3980.92 as a result of all the additional charges since September 2020. I need someone Senior at Supersonic to call me to resolve this issue, failing which, 1st June 2020 will be the date of cancellation of my contract with them.