Telkom changed my contract to a lower Tier without my consent

Around Feb 2020, I took a Telkom SmartBroadband Wireless Lte/Lte-A 200GB data contract which at the time stipulated I would receive 200GB anytime data and 200GB Night Surfer data. From Beginning July all of a sudden I am only receiving 200GB anytime data over 2 months (61 day) but still receive 200GB night surfer data every 31 days. I also realised all of a sudden on my online profile, they changed my product to: SmartBroadband Wireless 100GB Deal.

Is this legal? Because this was a 24 month contract, whereby I agreed to pay a certain amount and you agreed to give me the certain product during the duration of the contract. At no point whatsoever at the Telkom walk in centre did the sales agent tell me Telkom may change my product at anytime they wish without my consent whatsoever.