Contract downgrade

Just called Cell C and spoke to a lady by the name Adelaide, I wanted to change my contract from a 30GB to a 10GB as I saw on their online that they have it for R149 and wanted to downgrade. Adelaide downgraded my contract before confirming everything with me and before telling me the price, she later told me she has downgraded me and I will be paying R320p/m which is currently more than what I am paying. I want my contract to be downgraded to 10GB for R149 or be left as it was on 30GB I do not want that 10GB for R320. This was not professional of her, she did everything while in a hurry and did not wait for my confirmation, the kind of service received from Adelaide was very poor.