Supersonic is charging us incorrectly and is unwilling to communicate about it.

My initial experience with Supersonic was great. Our internet is amazing and they were super efficient. We haven't had any issues until today. I received a double invoice for December and January (the first invoices I have received since we joined them end of November). We signed up for the 200Gb package online (I have supporting emails) which should be R599 per month. BUT I am being invoiced R799 x2 for a 300 Gb package x2. When I asked them about it, they said they can only downgrade me in January. This is ridiculous as I did not sign up for the bigger package. Since sending them the proof of the 200Gb application, they have ignored my messages and have stopped responding completely. It is extremely disappointing after the great start I had with the company, they are now overcharging me R400 and not willing to communicate about the matter. I will have to go to the financial Ombudsman if they proceed with the debit order for R799 x2 vs. R599x2.