Why I Hate Vodacom

Purchased 10 gigs of data and 200 minutes on 26 December 2019 of airtime , over & above my contract. I did not renew my contract which expired on 31 Dec, and switched to prepaid. But Vodacom cancelled all additional data & airtime purchased, even though this should have expired on 26 January 2020. If I paid for the data & airtime, for that specific period, it belongs to me. I do not understand why Vodacom should cancel what has already been paid for. Despite logging query at the Vodacom store , calling their customer care, billings, subscriptions and whichever department I was transferred to, no one can explain why they cancelled what I paid for before the expiry date. This is why I HATE Vodacom.