Telkom Mobile - Upgrade to get blacklisted

I had a Telkom mobile contract for 2 years (R139 per month for 10GB), I was then contacted to upgrade my contract. I asked to be upgraded (R99 for 20GB). I received the new debicheck request for the new debit order which I accepted and suspended the existing one. After doing so, I received an invoice from Telkom Mobile stating that I owed the company R543. R99 and R139 for Oct 22, R99 for Nov 22 and account cancellation fees. I have tried contacting Telkom mobile via email but they just close off my requests as completed. They then send me a letter of demands saying they have contacted me numerous times to pay my outstanding balance - this is over the course of 3 weeks and they sent me 1 invoice to which I logged a query. Please contact me via phone so I can resolve this issue ASAP.