R612 charged with no reason

I tested out a 5G router but unfortunately had to return it within the month as the signal was weak. I received a full refund of my R1 000. However, the next month I got charged a random R612 on my credit card. This is after my account was completely cancelled. I chatted to someone on the website, sent 2 emails and loggeda query on the website - NO RESPONSE. While I try to understand that services are impacted during lockdown, it has been weeks since my first query and no resolution at all yet. I am R612 out of pocket for no reason during a time when I am already financially constrained. I expect a speedy refund!