I took a 2 years contract phone in August 2019, then October 2021,I upgraded the device

I took a 2 years contract phone in August 2019, then October 2021,I upgraded the device. However it have come to my attention that Telkom Mobile has been deducting device Obligation: R427.83 from my bill. They have been deducting this amount since 2021 October. I have reported this incident and however they don't want to resolve this issue. This is very frustrating because I'm paying for something I don't understand. I would like the money deducted since October to be refunded back to me, and this issue to be resolved.