Cell C not keeping it's promise

I have a contract with Cell C which was due for an upgrade on the 20th of April .Before it was due I went to about 4 cell c stores to upgrade they told me they don't have routers and all cell c stores don't have.I then wrote that I wanted to cancell my contract on Cell C twitter a lady called me to say that she can help me with an upgrade but for the fact that they don't have the package I was looking for she will put me on 10 gig month to month for R199 I agreed now when I check balance on Cell C app it says R400.05 which I am not going to pay because 1st I wanted to upgrade Cell C didn't have routers 2 They didn't have the package I wanted I asked for cancellation but the lady convinced me that I will pay R199 on month to month.So Cell C is at fault not me.Cell c will only debit R199 and cancell my contract nothing more than this.