Statement Dispute

I am dismayed and disgruntled at the level of service rendered by Telkom, despite being a paying customer who has never missed any payment. My mobile router (along with sim-card) was lost in October 2020 and I called in to cancel both. Luckily I had finished paying off my 2-year contract and was on a month-to-month contract. What perplexes me is that I was billed over 1k for the November statement due to activities on the sim-card which I reported to be ****** in 2020. I disputed the charge, and requested a full investigation to be conducted as I have not used nor been in possession of the device or sim-card since I reported it ****** yet I was still charged??? To this day, I have still not been contacted despite sending numerous emails and that irks my blood.