False advetising and miss information

I contacted CELL C in September to upgrade my contract and continue on a sim only option which i was paying R 189 per month, The Cell C agent confirmes the upgrade and we both agreed on a reduce amount of R149 for 10GB Day and 10 GB night. Yesterday CELL C sends me an SMS to pay R 304.85 which was not the agreement. I spoke to Sifiso at contracts department who said if i want to cancell the deal i must pay R 3000 for a contract that started on 10/10.2022.