Open line contract

I have been a client for Vodacom for over a decade now. 2023 I upgraded my contract to my surprise the sim card is an open line, whenever I run out of data they automatically load data which is sooo disgustingly expensive, for an example this month they topped the data with 200MB for over R600.

I have been trying to cancel this open line contract but they told me I must pay over R800.

I was never told about this open line contract from the beginning, had I known this I wasn’t going to take it. Vodacom is a ****ming us of our hard earned money