Unexpected Charges due to having a contract which I did not agree on

In 2018 I upgraded my contract and what I signed for was for a Pinnacle 1GB at R369 p/m and I took additional services which I cancelled as time passed, this month I reviewed my statement and realised that I am being charged additional charges for phonecalls made which are not included in the minutes that I are included in my contract and instead of paying R369 p/month for my contract I pay more than R700.00 per month. I phoned Cell C today and the consultant advised that I have an open line contract and I know that this is not what I signed for..... This means for 2 years I am paying more than what I am supposed to for a contract that I did not agree upon.