Wrong contract doesn't get fixed

I took out a data contract with Cell C and the lady who helped me signed me up for the wrong contract after I pointed with my finger to exactly the one I wanted. The deal was for 20gb data (10gb daytime and 10gb nite time) for R299 per month including a mobile router. She signed me up for the 20gb package at R249 per month, but it is 5gb during the day and 15gb at night. After I pointed it out to her she said I can change it after three months and will get back to me about changing it sooner. She didn't. After a week I phoned and someone else told me I have to wait one month and can only migrate from 21 Dec 2015. I went in on the 23rd and they said they would phone me at 1pm that same day because the deal wasn't available anymore. I am still waiting. After a week I phoned the call center (29 Dec 2015) and they logged the query and said they will phone me in 48hours. I am still waiting. It is not my fault that they gave me the wrong contract and now I am stuck in a contract I don't want. This is just ridiculous.