Handset Woes

I upgraded in September 2019, and since then I've been paying for 2 Handsets, and Vodacom informed me that I will pay for 2 handsets for 3 months, but now it's been September, October, November, December, January, and even on my current February invoice, I was charged again for 2 handsets, and when I phone to the call centre, they only inform me that the charges on the invoice is for the previous month, but then why charge me for the new Handset from September 2019. I don't get any acceptable answer on this, and it is really frustrating me a lot.