Contract was upgraded without my knowledge

My contract was upgraded last year April 2023 without my knowledge. I received 10gb modem and it still in a box I haven’t opened it yet. I reported it so many times that I didn’t upgrade my contract and I even went to Vodaworld Midrand. Till today I am still struggling to get help with the cancellation because I didn’t authorise any upgrade. Vodacom is debiting my account every month for the modem that I am not using.